2 questions about old fender bassman

[sunburst79]

This thread has got me thinking. My old Bassman 100 was sold to a buddy back in 1996. We used it in a band from 2013 until around 2018. Several years ago he lost his storage so it and the three cabs Bassman 100/Bassman VT 15/Bassman VT have been residing in my Bassment.

Since I started my little Redhead restoration project I've acquired a Bass 350 and a pair of Goliaths.

I'm thinking in a week or so i really ought to drag the Bassman 100 up and plug it into a Goliath III or both. It would be good for the amp to see some electrons flowing through it again.

So a Bassman 100 related question. My memory is the Bassman 100 and its specific matching Bassman 100 cab where sold as sets as the Bassman 100 with w cab and I have a vague memory of seeing a catalog page where the Bassman 100 with two cabs was listed as the Super Bassman 100 set. Not to be confused with the PS or Studio Series. Then later on sold with the Bassman VT 15 cabs when the Bassman 100 cab was discontinued or superseded.

Just wondering if my memories are correct because I'm sure someone knows.

And does anyone know what the VT In Bassman VT actually stands for? I can't remember if they are ported or not. If so my guess would be VenTed. If not perhaps Vintage or Vintage Tube.

After the CBS solid state amp debacle Fender did not offer solid state bass amps for quite some time. Other than the PS and Studio Bass models which where Ed Jahns creations the Bassman 100 was pretty much the Fender standard bearer bass head up into the 1980's and Rivera era. I'm lumping the Bassman 100 and 135 into the same bucket since the 135 replaced the 100 but was pretty much the same circuit or feature set sporting upgraded iron to generate more power.

The 100 and 135 use larger transformers than the 135 watt twin. I've heard the Bassman 100/135 described as a Twin Reverb minus the reverb and vibrato and with the DEEP switch. And while the Twin Reverb chassis also powered the SuperSix and QuadReverb's given the transformer changes it's not accurate to say it's a Twin Reverb minus Reverb/Vibrato.

Sorry. Long post. Anyone know what VT really stands for? The open back guitar extension cabs and the closed back cabs were OB and CB respectively. I'm guessing Vented. When introduced the VT was all new so Vintage seems rather unlikely.

 

[Wasnex]

This thread has got me thinking. My old Bassman 100 was sold to a buddy back in 1996. We used it in a band from 2013 until around 2018. Several years ago he lost his storage so it and the three cabs Bassman 100/Bassman VT 15/Bassman VT have been residing in my Bassment.

Since I started my little Redhead restoration project I've acquired a Bass 350 and a pair of Goliaths.

I'm thinking in a week or so i really ought to drag the Bassman 100 up and plug it into a Goliath III or both. It would be good for the amp to see some electrons flowing through it again.

So a Bassman 100 related question. My memory is the Bassman 100 and its specific matching Bassman 100 cab where sold as sets as the Bassman 100 with w cab and I have a vague memory of seeing a catalog page where the Bassman 100 with two cabs was listed as the Super Bassman 100 set. Not to be confused with the PS or Studio Series. Then later on sold with the Bassman VT 15 cabs when the Bassman 100 cab was discontinued or superseded.

Just wondering if my memories are correct because I'm sure someone knows.

And does anyone know what the VT In Bassman VT actually stands for? I can't remember if they are ported or not. If so my guess would be VenTed. If not perhaps Vintage or Vintage Tube.

After the CBS solid state amp debacle Fender did not offer solid state bass amps for quite some time. Other than the PS and Studio Bass models which where Ed Jahns creations the Bassman 100 was pretty much the Fender standard bearer bass head up into the 1980's and Rivera era. I'm lumping the Bassman 100 and 135 into the same bucket since the 135 replaced the 100 but was pretty much the same circuit or feature set sporting upgraded iron to generate more power.

The 100 and 135 use larger transformers than the 135 watt twin. I've heard the Bassman 100/135 described as a Twin Reverb minus the reverb and vibrato and with the DEEP switch. And while the Twin Reverb chassis also powered the SuperSix and QuadReverb's given the transformer changes it's not accurate to say it's a Twin Reverb minus Reverb/Vibrato.

Sorry. Long post. Anyone know what VT really stands for? The open back guitar extension cabs and the closed back cabs were OB and CB respectively. I'm guessing Vented. When introduced the VT was all new so Vintage seems rather unlikely.

I think you have some errors in this. I am not an expert, but I will try to cobble up a good answer.

The Super Bassman was 100W, but it had a taller headcase and was a non master amp. It came out in 1969.

I believe the Bassman 100 came out in 1972. Back to the short headcase and a Master was added.

AFAIK all Super Bassman and Bassman 100s are 4 ohms only. You can run a second matching cab, but it causes an impedance mismatch.

The Bassman 135 continued with the short headcase and master and came out in 1977. It also had several changes to the output section. The output section is wired in an "ultra linear" configuration and the output transformer has 4 ohm and 8 ohm taps. The extension output switches the impedance to 8 ohms and connects the speakers in series. So the expected load of each cab is 4 ohms.

Some mod the 135 by disconnecting the screens from the output transformer and powering them the regular way. This is supposed to make it sound more like the older amps. For clean bass, my guess is it might be better stock. However, if you like pushing the output section into drive territory, it may be better to mod the amp.

There may be other differences between the preamp.

 

[KenB]

…And does anyone know what the VT In Bassman VT actually stands for? I can't remember if they are ported or not. If so my guess would be VenTed. If not perhaps Vintage or Vintage Tube.


Sorry. Long post. Anyone know what VT really stands for? The open back guitar extension cabs and the closed back cabs were OB and CB respectively. I'm guessing Vented. When introduced the VT was all new so Vintage seems rather unlikely.

V. T. stands for "Vacuum Tube"

The V. T. BASSMAN 15 cabs were 4 ohm cabs (2x15") designed for use with the tube heads that required a 4 ohm load (see above post).

 

[Bob_Ross]

AFAIK all Super Bassman and Bassman 100s are 4 ohms only.

My recollection of the 1972 Bassman 100 was that it was 4 ohms *minimum* …it would happily play into an 8 ohm load, albeit at reduced power.

So yeah, no point in adding a second cab & jumping through hoops to wire them in series just to get an EVEN MORE underpowered bass rig!

I just felt the Semantic Police approaching when I read "only"

 

[Wasnex]

My recollection of the 1972 Bassman 100 was that it was 4 ohms *minimum* …it would happily play into an 8 ohm load, albeit at reduced power.

So yeah, no point in adding a second cab & jumping through hoops to wire them in series just to get an EVEN MORE underpowered bass rig!

In general, tube amps expect a certain impedance. Tubes have a relatively high output impedance and speakers have a relatively low input impedance. The output transformer serves as a go-between; in essence matching the high impedance of the tubes to the low impedance of the cab. If the matching is off, the amp makes less power and there is more wear and tear on the amp and tubes.


The schematic for the Bassman 100 says 4 ohms.

Normally vintage Fender amps were sold with a specific cab that showed the amp the expected loud. A matching extension cab could also be used, but AFAIK this typically resulted in an impedance mismatch. So a Bassman 100 pushing two of the pyramid cabs would see a 2 ohm load. A lot of people say Fender amps of this era are safe if the load is one order to high as well. So the Bassman 100 is assumed safe with an 8 ohm load, as you suggest.

IMHO it's still best to show the Bassman 100 exactly the expected load (4 ohms).

I just felt the Semantic Police approaching when I read "only"

Sorry I wrote inartfully . What I meant is the Super Bassman and Bassman 100 only came with 4 ohm output transformers. AFAIK they were not offered with an 8 ohm OT. This is in contrast to the blackface era Showman and Dual Showman amps which were 8 ohms and 4 ohms respectively. I believe Fender was not necessarily 100% consistent with this naming convention. So it's a good idea to actually check the transformer codes in the amp to confirm it's set up for 4 ohms or 8 ohms.

 

[rockear]

Lots of great informative posts in this thread. I just wanted to throw in my 2 ¢ as someone who's main amp has been a '69 Super Bassman for a couple decades...

I think a lot of the reputation that these amps have for being lackluster or anemic comes from the speaker technology that was prevalent when they were new. Old guitar cabs can sound great. Bass cabs have come a long way in the last 50 years. This thing really sings through a modern cab, particularly if you turn it up enough to get a little crunchy.

I've never had an issue with insufficient volume. Any gig that needs more than what this can deliver will definitely offer PA support.

 

[Wasnex]

The 100 and 135 use larger transformers than the 135 watt twin. I've heard the Bassman 100/135 described as a Twin Reverb minus the reverb and vibrato and with the DEEP switch. And while the Twin Reverb chassis also powered the SuperSix and QuadReverb's given the transformer changes it's not accurate to say it's a Twin Reverb minus Reverb/Vibrato.

???

Per the schematics, Bassman 135 and Twin Reverb SF135 use the exact same transformers. OT is 013691 and PT is 013692

https://www.prowessamplifiers.com/schematics/fender/twin_reverb_sf_135_schem.pdf

https://www.prowessamplifiers.com/schematics/fender/bassman_135_schem.pdf

SF135

Bassman 135

 

[sunburst79]

I'm curious. The Bassman 100 probably used different transformers than the UL amps.

I had the UL 135 TR and that amp had the best clean sound of any amp I've ever owned. I wish I'd kept it for that reason.

The Bassman 100 head is really terribly unbalanced in a way the Twin wasn't. The Twin is long gone but I'd have sworn the Bassman 100 had a heavier PT and lager OT. I do not remember the Twins transformers as being as large. But I can believe they used the same iron on all the Ultra Linear Amps.

That looks like a multi tap transformer since the Vibrasonic is 8 ohms. But it's also connecting different.

I need to check the ohms on the Bassman 50 cabs I have. I have no idea if they were 8 or 4 ohms. But if they were 8 ohms each and connecting the pair put the connection into parallel than that's the 4 ohms the transformer wants to see. Vintage Bassman 50 cabs vs Bassman 100 can. I'll just say the consensus was the Bassman 50 cab(s) sounded better than the Bassman 100. Which was pretty wooly and undefined. Regardless of where you stood. But it was also exceptionally beamy in that all those angled drivers focused on a single point.

The amp was fine. The matching cab was kind of a dud IMO but the rest of the band universally agreed that the Bassman 50 cabs sounded better. So not just my opinion.

You could hear the Bassman fine in my second band. With the pair of Bassman 50 cabs. You could still hear it with the Bassman 100 cab. It was just very fuzzy sounding. Indistinct would be apt.

I've never heard of it being done so I'm willing to bet the transformers windings aren't right. But I wonder if a 135 could be modded for 6550's? Again probably not. AFAIK the whole ultra linear idea was borrowed from HiFi and Ampeg. I doubt 6550's would give more watts or much more. But the headroom might go up. I've never heard of it being done and if possible I think someone would have tried that in the last 48 years. But a Bassman 160 doesn't seem like a bad idea.

I converted a drip edge Bandmaster to the universal tube basing and it didn't sound very different with EL34s. But it worked and biased just fine.

A 135 watt Twin with a Deep switch would be cool. It's not like the amp needed a bright switch.

 

[Wasnex]

I'm curious. The Bassman 100 probably used different transformers than the UL amps.

I had the UL 135 TR and that amp had the best clean sound of any amp I've ever owned. I wish I'd kept it for that reason.

The Bassman 100 head is really terribly unbalanced in a way the Twin wasn't. The Twin is long gone but I'd have sworn the Bassman 100 had a heavier PT and lager OT. I do not remember the Twins transformers as being as large. But I can believe they used the same iron on all the Ultra Linear Amps.

That looks like a multi tap transformer since the Vibrasonic is 8 ohms. But it's also connecting different.

I need to check the ohms on the Bassman 50 cabs I have. I have no idea if they were 8 or 4 ohms. But if they were 8 ohms each and connecting the pair put the connection into parallel than that's the 4 ohms the transformer wants to see. Vintage Bassman 50 cabs vs Bassman 100 can. I'll just say the consensus was the Bassman 50 cab(s) sounded better than the Bassman 100. Which was pretty wooly and undefined. Regardless of where you stood. But it was also exceptionally beamy in that all those angled drivers focused on a single point.

The amp was fine. The matching cab was kind of a dud IMO but the rest of the band universally agreed that the Bassman 50 cabs sounded better. So not just my opinion.

You could hear the Bassman fine in my second band. With the pair of Bassman 50 cabs. You could still hear it with the Bassman 100 cab. It was just very fuzzy sounding. Indistinct would be apt.

I've never heard of it being done so I'm willing to bet the transformers windings aren't right. But I wonder if a 135 could be modded for 6550's? Again probably not. AFAIK the whole ultra linear idea was borrowed from HiFi and Ampeg. I doubt 6550's would give more watts or much more. But the headroom might go up. I've never heard of it being done and if possible I think someone would have tried that in the last 48 years. But a Bassman 160 doesn't seem like a bad idea.

I converted a drip edge Bandmaster to the universal tube basing and it didn't sound very different with EL34s. But it worked and biased just fine.

A 135 watt Twin with a Deep switch would be cool. It's not like the amp needed a bright switch.

Yes the ultralinear transformer is different. Sunn 2000S is ultralinear. I believe this applies to all of the 1000 Series sunn amps. Previous gen Ashdown Small Block 427 and BTA amps also use ultra linear. Current Ashdown CTM100, CTM200, and CTM300 is ultralinear.

My TFL5005D Showman Reverb is also pretty unbalanced. Pretty much same vintage as the Super Bassman. The Showman is basically a Twin in head form. Schematic shows a different OT number than the Super Bassman and Bassman 100. It may be equivalent and the difference is simply Pre VS Post CBS part numbers.

6550s pull more heater current than 6L6GC, so probably unwise to try them in these amps without installing a additional heater transformer.

 

[sunburst79]

Yes the ultralinear transformer is different. Sunn 2000S is ultralinear. I believe this applies to all of the 1000 Series sunn amps. Previous gen Ashdown Small Block 427 and BTA amps also use ultra linear. Current Ashdown CTM100, CTM200, and CTM300 is ultralinear.

My TFL5005D Showman Reverb is also pretty unbalanced. Pretty much same vintage as the Super Bassman. The Showman is basically a Twin in head form. Schematic shows a different OT number than the Super Bassman and Bassman 100. It may be equivalent and the difference is simply Pre VS Post CBS part numbers.

6550s pull more heater current than 6L6GC, so probably unwise to try them in these amps without installing a additional heater transformer.

I never owned a TFL 5005D. I wish I'd bought one when they were more affordable.

I always thought the model number on the front panel was odd. I finally looked that up recently and it seemed like something that should be on the back panel.

But it tells you something about the construction and the power transformer.

I actually assumed for years that was some CBS secret code for the infamous CBS mod and avoided them.

I assume heater transformers are still available. Haven't check in about 3 decades. If one could find a Bassman 135 and the windings are right let's just say I think that would be interesting. Although I don't really do mods like that to nice clean old amps. But there are plenty of trashed Master Volume 135 watt Twins out there as basket cases. A few preamp components to convert it to Bassman specs and you'd be in the ball park. Of course a head case with the vent would be helpful. And you'd have to live with vibrato and reverb but that wouldn't be hard.

Something I noticed is that not all Bassman 135's I've seen have the extra chassis vent. That may have been an update.

 

[Wasnex]

I actually assumed for years that was some CBS secret code for the infamous CBS mod and avoided them.

My Showman Reverb is one of the early ones (drip edge), so it pretty close to blackface Twin Reverb spec. I believe the bias has been reconfigured to blackface spec. Not sure of other common blackface revision. It sounds very close to the blackface Twin Reverb I learned to play through. Perhaps a bit softer as it's setup with 5881 rather than 6L6GC.

 

[sunburst79]

I love old black plate 5881's. In the right circuit they sound fantastic. Definitely like those over the old Fender branded STR 6L6GC.

I just thought it was funny TFL stood for Teflon jacketed wire and the suffix was the input voltage. D being Domestic. Not something they needed to call out under the amps name on the front panel.

I'm assuming you mean they turned a hum balance pot into a bias voltage pot? The real CBS mod from what I understand was some caps by or on the tube sockets to filter out ultrasonic parasitic oscillations. I mean they changed quite a few small things but only for a short while.

 

[Wasnex]

I'm assuming you mean they turned a hum balance pot into a bias voltage pot? The real CBS mod from what I understand was some caps by or on the tube sockets to filter out ultrasonic parasitic oscillations. I mean they changed quite a few small things but only for a short while.

I haven't done any blackface revisions myself so I don't know what has been done. I have replaced a couple of small signal tubes and a leaky tone stack. Other than that, it sounds fine so I have left it alone. I did an inspection years ago, but didn't document my findings other than writing it appears to have been converted to blackface spec. My impression is it's pretty much a blackface Twin Reverb in a headcase. I believe it's a 68 so I doubt much of a revision was required.

Per the schematic, the amp originally had a bias balance control. This allows you to balance the tube current on opposite sides of the OT, but doesn't allow you to set bias. I did check the bias and my recollection is the control has been rewired to function like a traditional bias pot.

I did some Googling on the transformer question last night. I found comments that said the output transformer (OT) in the Super Bassman and Bassman 100 is physically bigger than the OT in the Twin and Showman Reverb amps. Some comments suggest the Bassman transformer extends the low frequency cutoff lower down into the 30hz range and also rolls of the highs sooner. I don't know if this is accurate. I have heard a Bassman 100, but that was almost 50 years ago. My memory is it sounded good, but I hadn't even bought my first bass yet, so not really a qualified opinion at the time.

 

[sunburst79]

I haven't done any blackface revisions myself so I don't know what has been done. I have replaced a couple of small signal tubes and a leaky tone stack. Other than that, it sounds fine so I have left it alone. I did an inspection years ago, but didn't document my findings other than writing it appears to have been converted to blackface spec. My impression is it's pretty much a blackface Twin Reverb in a headcase. I believe it's a 68 so I doubt much of a revision was required.

Per the schematic, the amp originally had a bias balance control. This allows you to balance the tube current on opposite sides of the OT, but doesn't allow you to set bias. I did check the bias and my recollection is the control has been rewired to function like a traditional bias pot.

I did some Googling on the transformer question last night. I found comments that said the output transformer (OT) in the Super Bassman and Bassman 100 is physically bigger than the OT in the Twin and Showman Reverb amps. Some comments suggest the Bassman transformer extends the low frequency cutoff lower down into the 30hz range and also rolls of the highs sooner. I don't know if this is accurate. I have heard a Bassman 100, but that was almost 50 years ago. My memory is it sounded good, but I hadn't even bought my first bass yet, so not really a qualified opinion at the time.

Thats my memory. That the transformers bigger. I sold rhe UL TR many years ago so I can't compare. Also the Twin will have better balance because the weight of the speakers seem to level it out.

What a joy it was carrying a Twin down three flights of stairs and 250 feet across the parking lot and reversing the process at the end of the night.

Might be wrong (as I often am) but I think the name of that pot may have changed from Hum Balance to Output Tube matching. If they had kept the bias vintage pot and added the hum balance control that would have been pretty useful.

Fender knew that quality tubes would one day be harder to source.

 

[Wasnex]

Might be wrong (as I often am) but I think the name of that pot may have changed from Hum Balance to Output Tube matching. If they had kept the bias vintage pot and added the hum balance control that would have been pretty useful.

Bias and hum balance are usually different things. AFAIK the CBS bias circuit is often referred to as bias balance. On some schematics it's labeled "Output Tube Matching." The control is not a regular potentiometer, it's tapped, which means it has an extra terminal. I.E. four terminals instead of three.

Balancing the tube current across the transformer does have an impact on hum. If the tubes are out of balance the amp will produce a sound I describe as sort of a dull, low frequency roar.

Hum balance also adjusts hum (DUH), but it usually addresses a sound that is brighter and more wiry. There are several different types of circuit used for hum balance, and AFAIK none of them affect bias. AFAIK they typically work by adjusting the relationship between signal ground and chassis ground.

If you look at the Bassman 135 schematic is has both hum balance and Output Tube Matching controls. https://schematicheaven.net/fenderamps/bassman_135_schem.pdf

AFAIK hum balance was added at some point in the silverface era. I don't believe any blackface amps used them. My early silverface amp does not have a hum balance control

A fairly common mod to reduce hum is to add an artifical center tap on the heater supply

 

[Freight Train]

You make some good points, but we need to consider the price. The only currently made all-tube Bassman (the Super Bassman) costs more than 4 times as much as a used 70s Bassman 100. The same goes for other currently made 300w tube amps. At least this is the case in my part of the world. And yes, the output tubes make a difference, so I won't even consider the hybrid Bassman 800 in this context. I have yet to play any hybrid amp that delivers the "feel" (dynamics) of an all-tube amp. As for the Rumble amps, they are good amps for what they are, but (for better or worse) they will NOT give you the classic tube amp tone/feel of a Bassman 100. Not even close.

Of course, the currently made 300w all-tube Super Bassman is a far more powerful amp than the 70s Bassman 100. But it's also a very different amp, with a different tone. For better or worse, nothing will sound like a vintage Bassman. There's also the matter of how much wattage you really need. Tube amps tend to be at their best when they're pushed close to (or beyond) the point of breakup. This is ONE of the reasons why I hate playing SVT rigs on small club stages. With SVTs on a small stage I simply cannot turn up the volume to where the amp actually sounds great. For this reason I typically bring a 100w or 200w tube amp to most gigs, depending on how much power I think I will need. With all-tube amps it's not a matter of "more power = better". It's all about finding an amp with an output volume that matches your actual needs.

And that's the reason why something like a 70s Bassman 100 can, at least for some players, be a BETTER choice than a more powerful all-tube amp.

I'm also surprised to see so many negative comments about the TONE of the Bassman 100. There's even one post than mentions the Peavey Mark IV as an upgrade on the Bassman 100. Don't get me wrong, we all have different taste and I totally respect that, but from MY point of view I honestly can't undestand how anyone would consider a Peavey Mark IV an upgrade on a Bassman 100 in any way whatsoever. I started out on one of those Peaveys. Then I got my Bassman 100 and that was IT as far as I was concerned. I instantly knew I would never play anything other than a tube amp ever again. I still don't. At least not in any situation where I can bring my own backline. No solid state or hybrid amp I've tested nso far has give me the tone, and perhaps more importantly the "feel" (dynamics) of a proper tube amp. I'm not saying one is BETTER than the other. There are certainly some advantages with modern Class D amps. I'm simply saying they're DIFFERENT, and if you're looking for the tone/feel of a tube amp, that's what you'll need.

Sure, the Bassman 100 is a bit mid scooped, which may not be ideal for all players or all styles of music. It's not even my personal favorite. Like I mentioned before, I'm more into vintage British tube amps with a stronger mid presence. But the Bassman 100 delivers a great, CLASSIC tube amp tone. The fact that I still own mine says it all for me. My old Peavey Mark IV is long gone, and I haven't missed it for a second.

For the right player, and with the right cab, a Bassman 100 can still be a FANTASTIC amp.

And just to be clear, when I say "the right cab" I definitely don't mean the original Bassman cabs from back in the day, they're very poor by today's standards. The amps are still great, the cabs are not.

+1 on this. I regularly gig on everything from dive bar to festival stages with either a 50 watt Ampeg PF-50T with one or two PF-115HE cabs, or the 100/25 watt Bassman 100T with the Bassman 410Neo cab. I realize sonically these two are as different from the 70's Bassman amps as they are from each other, so I'm talking strictly from what tube bass amps in this power range can do. As I've said before, it seems that most of the reports I see of bassists running out of gas with lower-powered tube rigs trying to match volumes with guitar and/or drums is in the REHEARSAL ROOM. I don't know where people are playing otherwise where FOH and monitor support would not be available in medium to large venues. It's not a matter of mic'ing up a horrible sounding clipping underpowered solid state amp, rather as S.F. Sorrow said it is specifically using lower-powered tube amps so you can crank the amp to achieve that sweet spot in the power tubes at a reasonable volume. And then running that through FOH or monitors as needed. So the low power is a feature, not a bug, as they say. This has never been a problem on any stage I've played with either of my rigs, which I'm going on 12 years since I switched to lower-powered all-tube. But if I were unfortunate enough to play in a band with a guitarist or two who have to blow full volume in the rehearsal room, drummer likewise, I don't know if either rig could do that. Probably not. But I don't care, I wouldn't be in that situation.
But, and it's a big but, just because 50 - 100 watt tube amps can perform as above, that doesn't mean you'll like the tonal quality of the vintage Bassman amps even with a modern, efficient cab. It will not be like a class D amp, which most will give you a LOT of clinical, clean, flat, vanilla, 2 dimensional watts, and then you pretty much have to add processing to get any character out of it (IME!) The Bassman on the other hand will have all kinds of baked-in character and color that seemingly organically changes as the volume is varied. But unfortunately you won't know if that's your bag until you try it.