Fender Bassman 100T Chapter 3

[GG7]

That's a great tip GG. Mine is set to be delivered Thursday...can't wait!

That is a good question though. Are most of you guys running your power section at "normal" or are you pushing them. To be honest, I couldn't hear much difference on my SB300 but I'd bet it was because I didn't push the power section enough. That and the fact it had the 6550's rather than the 6L6's.

Thanks Husky and CONGRATS on your pending 100t arrival!

And I think an early WELCOME to the 100t CLUB! is in order!

You're right that the 6550 is a lot more power tube than a 6L6, and I don't think they get driven nearly as hard as the 6L6s do in the 100t circuit at what I would consider practice and recording volumes, so I don't think you will notice as much nuance with plate voltage tweaks at these volume/dB ranges.

You would probably need to be running the SB at concert volumes to see the same effects.

I've messed around with my amp a whole bunch and I am still discovering new little tricks you can do with manipulating the various power controls coupled with the tone stacks.

My latest project is trying to find the optimum active tone stack setting for the Rickenbacker 4003. I'm not getting that classic Rick BITE through the vintage channel which I have optimized for my J Basses and I don't want to mess with that tone stack.

That leaves the active side, and I have yet to find the "sweet spot" for this bass yet. I've got Nickel Lo-riders on there and they are brand new, so I am not going to start sweating this yet since I know for a fact that these strings are weak in the low end and upper mids until they are broken in.

Still... I think I am going to create a thread asking for 100t active channel settings for a 4001/4003, and see what others are doing to get the classic Ric sound.

Whats really funny is that right now my 64 American Vintage Jazz Bass through the vintage channel is doing a far better job at sounding like a 4003 than my 4003 is! lol!

 

[Lia_G]

Hmmm ... I always thought the 25 watt setting ran full plate voltage but only on one 6l6, cutting three of the power tubes out of the circuit. Does it actually run all four 6l6s just at reduced voltage instead?

Liam

 

[GG7]

Hmmm ... I always thought the 25 watt setting ran full plate voltage but only on one 6l6, cutting three of the power tubes out of the circuit. Does it actually run all four 6l6s just at reduced voltage instead?

Liam

Don't think it just runs one and shuts the others down. That would put an undo amount of stress on a single tube. Pretty sure it runs all four at a reduced voltage, but I am not positive of that, it just makes more sense resource wise to keep the load balanced across all four.

I had the back off mine for a long time while I was doing all the tube rolling, and the times I was running in 25w mode, all four tubes looked like they were glowing at the same brightness, but that brightness was noticeably dimmer than when they are running at full output power at 100w.

 

[TorontoAlex]

Hey guys, this is probably more of an observation than an issue per say, however I'd like some other opinions if possible. I've found that the active channel is noticeably quieter than the passive channel, if the volumes are the same on each channel. Last night at practice I had the passive at about 6, and to get up to the same levels on the active I was at a hair over 8. I didn't notice this before, and although it may just be me, I could have sworn the active was louder than the passive a few months ago.
Has anyone experienced the same? I would have assumed that the active would have been louder (or at least perceived to be that way), owing to the harmonics that the OD produces. I should mention that this is with using the same bass in each channel.
Another maybe related question; I know that the 100t has two 12AX7 tubes in the pre, does this mean that one tube is assigned to each channel? Or does each channel run through both? If it's the former, could a faulty tube be the culprit?
Just to be clear, I love this amp, and will continue to use both channels, I'm just finding this a bit odd. Thanks all.

 

[Freight Train]

I also noticed the active channel has a bit lower gain. That really doesn't mean anything I don't think. Different preamp designs, different gains. Don't remember mine being quite as radical as 2 notches on the gain. Seemed more like 4 on the passive channel equaled 5 on the active channel. I'll recheck and let you know how mine works.
1/2 of 12AX7 V1 is the first gain stage for both channels (Brings the instrument level up to line level). The second half of V1 is used in the Bright circuit (pull treble eq knob) for the vintage channel. Both halves of V2 are used in the active channel's overdrive circuit.

 

[husky123]

So another question....trying to knock the cobwebs from my SB "layoff".

The overdrive channel: you can blend a clean tone with not? Not the tone from the vintage side, meaning that EQ (vintage) does not affect the blending in the OD? You just get a pure "studio-esque" clean tone to blend in with the OD's active EQ?

 

[TorontoAlex]

Thanks Freight Train for that, very helpful.

 

[Freight Train]

So another question....trying to knock the cobwebs from my SB "layoff".

The overdrive channel: you can blend a clean tone with not? Not the tone from the vintage side, meaning that EQ (vintage) does not affect the blending in the OD? You just get a pure "studio-esque" clean tone to blend in with the OD's active EQ?

You're right, the two channels are completely discreet. The blend does not blend the vintage channel with the overdrive channel, so nothing you do on the vintage channel gain or eq will affect the overdrive channel, and vice-versa.
You're almost right on the second point. The blend control blends the clean bass input, just after the V1 preamp gain stage, with the output of the overdrive circuit, but BEFORE the active eq, so you are eq'ing both the clean and overdriven bass signals after they've been blended to taste.

 

[husky123]

You're right, the two channels are completely discreet. The blend does not blend the vintage channel with the overdrive channel, so nothing you do on the vintage channel gain or eq will affect the overdrive channel, and vice-versa.
You're almost right on the second point. The blend control blends the clean bass input, just after the V1 preamp gain stage, with the output of the overdrive circuit, but BEFORE the active eq, so you are eq'ing both the clean and overdriven bass signals after they've been blended to taste.

Bang! Thanks, that's exactly what I was looking for.

 

[idoru]

Went and exchanged my head this morning - so far, so good with the replacement!

 

[NOLA Bass]

The first track from my new band is online. This is actually a band that did a metal tribute cover band for the last decade. We kind of burned out and shelved it to start an original project. We are heading back into the studio later this month to finish the debut album, but gave a track to the Intergalactic Krewe of Chewbacchus for their first Benefit CD (it is a Mardi Gras marching parade in New Orleans with a Star Wars, etc. theme - think Comic Con meets Mardi Gras - actually had Peter Mayhew, the actor that played Chewbacca as the Grand Marshall in 2013).

In the studio, I used my Spector 435LX (strung to C standard tuning) into 2 channels: A clean signal through and Avalon U5 and we mic'd my 100T through a vintage Ampeg 810. I used the overdrive channel with a fair amount of grit dialed up. This was before I switched to the Winged C power tubes, so it was completely stock.

http://chewbacchus.bandcamp.com/track/asphyxiation

Hope you like it.

 

[arock]

Don't think it just runs one and shuts the others down. That would put an undo amount of stress on a single tube. Pretty sure it runs all four at a reduced voltage, but I am not positive of that, it just makes more sense resource wise to keep the load balanced across all four.

Yes, I believe this is documented in the manual. All four output tubes are running at 1/2 the plate voltage when in 25W mode. Output power depends on the square of the voltage so that's why power goes down by a factor of 4 when voltage is cut by a factor of 2.

 

[Lia_G]

Cool. Makes sense.

Liam

 

[rbud2003]

I've been reading this thread (all three parts!) and I'm considering getting the 100T. It seems like a good fit for my gig, practice, and recording needs.

Before pulling the trigger, I have a question about my intended use of this head for gigs.

My band has a quality PA system with good monitors and a sub-woofer. With that in mind, here is what I was thinking of doing with the 100T.

- DI to the PA with the output coming from after the power section (this is one of the features that got my looking at this head)
- Get my bass sound from my floor monitor or in-ear
- If needed, use a 15" cab to send some extra bass oomph to my drummer.

My band has 2 guitarists that know about keeping stage volume under control. My drummer, bless him, does too but can go caveman at times. My current rig is Peavey VB-2 (200w) going through either a single 15" or a 15"/1x12" stack.

Does my intended use of the 100T seem reasonable? Thanks in advance for comments, suggestions, etc.

 

[GG7]

Yes, I believe this is documented in the manual. All four output tubes are running at 1/2 the plate voltage when in 25W mode. Output power depends on the square of the voltage so that's why power goes down by a factor of 4 when voltage is cut by a factor of 2.

There ya go! Didn't remember reading it in the manual, so I didn't check there! LOL!

Thanks for clearing that up! Explains why visually, all four tubes were showing equal brightness in their filaments but not as hot as when running at full boogie!

 

[GG7]

Another maybe related question; I know that the 100t has two 12AX7 tubes in the pre, does this mean that one tube is assigned to each channel? Or does each channel run through both? If it's the former, could a faulty tube be the culprit?
Just to be clear, I love this amp, and will continue to use both channels, I'm just finding this a bit odd. Thanks all.

First to answer your question.... V1 and V2 is part of the preamp gain stage for BOTH channels of the amp. Both the vintage and active use the same two preamp tubes. V1 is traditionally considered the most important when choosing which tube to put where, but I personally consider both V1 and V2 to be equally vital in the sound of the amp, and try to run two closely matched AX7s here. Treat them like you would a pair of power tubes and you will never go wrong!

The distortion that gets injected when using the GAIN and BLEND controls is definitely preamp tube in origin, not power tube based.

I say this with this much confidence because while tube rolling previously, the tone of the active channel varied considerably when swapping in and out various AX7s. If I left the blend and gain up on that channel and A - B ed between different brands and low to high GM testing results, that distortion sounded way different.

Used and tired AX7s I tried in the amp produced far more distortion on this channel at lower level settings than new or above new testing sets.

The Mullard Blackburns I am running in V1 and V2, actually produced the warmest distortion in this regard and was one of the reasons I went with them in the end.

This is an area where running a good medium to high testing RCA, GE, Amperex, Mullard or Telefunken in V1 and V2 can really make an audible difference for you. And don't forget about the lonely 12AT7! He's just as important as the AX7s to your amp's performance if not more so! This PHASE INVERTER tube should be of the highest quality possible, and you want to find a tube with even testing results on the T1 and T2 (Triodes). Since this tube sends the signal on to the four 6L6s, it is important to have an AT7 that is in tip top operating condition and gives those power tubes the best signal strength and quality possible!

I found that RCA blackplates, GE and Raytheon AT7s from the late 50s though the 60s had the highest ratio of balanced plates and highest testing results. I ended up going with a RCA BlackPlate AT7 with a date code of 1957.

Differences are there but harder to hear so clearly if you just audition through the vintage channel at normal/typical operating settings.

 

[GG7]

I've been reading this thread (all three parts!) and I'm considering getting the 100T. It seems like a good fit for my gig, practice, and recording needs.

Before pulling the trigger, I have a question about my intended use of this head for gigs.

My band has a quality PA system with good monitors and a sub-woofer. With that in mind, here is what I was thinking of doing with the 100T.

- DI to the PA with the output coming from after the power section (this is one of the features that got my looking at this head)
- Get my bass sound from my floor monitor or in-ear
- If needed, use a 15" cab to send some extra bass oomph to my drummer.

My band has 2 guitarists that know about keeping stage volume under control. My drummer, bless him, does too but can go caveman at times. My current rig is Peavey VB-2 (200w) going through either a single 15" or a 15"/1x12" stack.

Does my intended use of the 100T seem reasonable? Thanks in advance for comments, suggestions, etc.

Sounds like a good well thought out application for the amp, that it can easily handle!

The DI from the 100t is unique in that the signal it sends is actually downstream of the four 6L6 GCs! They have a power soak in there, and so what you send to the board sounds a lot closer to the tone coming out of the amp's speaker output than the typical preamp only DI feed of other amps.

How you run the speakers off the head might be something you want to decide on through trial and error, since there is no way to know on paper, which approach you will like best for your stage monitor setup. Either a traditional monitor feed from thr FOH or monitor mixer, or a 410 NEO cab or something under the amp onstage.

Obviously, from a cosmetic perspective, nothing looks cooler than a Fender Bassman STACK!

 

[Freight Train]

First to answer your question.... V1 and V2 is part of the preamp gain stage for BOTH channels of the amp. Both the vintage and active use the same two preamp tubes. V1 is traditionally considered the most important when choosing which tube to put where, but I personally consider both V1 and V2 to be equally vital in the sound of the amp, and try to run two closely matched AX7s here. Treat them like you would a pair of power tubes and you will never go wrong!

The distortion that gets injected when using the GAIN and BLEND controls is definitely preamp tube in origin, not power tube based.

I say this with this much confidence because while tube rolling previously, the tone of the active channel varied considerably when swapping in and out various AX7s. If I left the blend and gain up on that channel and A - B ed between different brands and low to high GM testing results, that distortion sounded way different.

Used and tired AX7s I tried in the amp produced far more distortion on this channel at lower level settings than new or above new testing sets.

The Mullard Blackburns I am running in V1 and V2, actually produced the warmest distortion in this regard and was one of the reasons I went with them in the end.

This is an area where running a good medium to high testing RCA, GE, Amperex, Mullard or Telefunken in V1 and V2 can really make an audible difference for you. And don't forget about the lonely 12AT7! He's just as important as the AX7s to your amp's performance if not more so! This PHASE INVERTER tube should be of the highest quality possible, and you want to find a tube with even testing results on the T1 and T2 (Triodes). Since this tube sends the signal on to the four 6L6s, it is important to have an AT7 that is in tip top operating condition and gives those power tubes the best signal strength and quality possible!

I found that RCA blackplates, GE and Raytheon AT7s from the late 50s though the 60s had the highest ratio of balanced plates and highest testing results. I ended up going with a RCA BlackPlate AT7 with a date code of 1957.

Differences are there but harder to hear so clearly if you just audition through the vintage channel at normal/typical operating settings.

That is not correct. 1/2 of V1 is the first gain stage for both channels. The second half of V1 is in the "bright" circuit of the vintage channel. Both halves of V2 are in the overdrive circuit of the active channel. So only V1 affects both channels. Plus I don't think of all the misconceptions people have had about the amp that anyone thought the blend control could possibly have anything to do with the output of the power tubes.

 

[GG7]

Didn't know that V2 had no involvement with the Vintage channel. That is a departure. Explains why the distortion personality was most obvious when auditioning the AX7 in V2 with the active channel and with the blend and gain up.

Don't remember now where I saw the confusion about the power tubes being involved in the GAIN control. Might not have even been in this thread.

Anyway... Thanks for the info! When I get a chance, I am going to give my buddy at Fender a call and get all these details confirmed/clarified, so I know exactly what is going on with all these features and how they relate to the various tube positions etc.

It would help me to know for sure, cause I am planning to put together several complete sets of NOS Bassman 100t preamp and power tube packages for sale later this year.

I've got more here than my amp is ever going to go through, and I think other 100t owners might appreciate buying their vintage tube set from someone who actually owns and uses the same amp, and doesn't just sell and price based on test results etc.

Cheers.

 

[Freight Train]

Didn't know that V2 had no involvement with the Vintage channel. That is a departure. Explains why the distortion personality was most obvious when auditioning the AX7 in V2 with the active channel and with the blend and gain up.

Don't remember now where I saw the confusion about the power tubes being involved in the GAIN control. Might not have even been in this thread.

Anyway... Thanks for the info! When I get a chance, I am going to give my buddy at Fender a call and get all these details confirmed/clarified, so I know exactly what is going on with all these features and how they relate to the various tube positions etc.

It would help me to know for sure, cause I am planning to put together several complete sets of NOS Bassman 100t preamp and power tube packages for sale later this year.

I've got more here than my amp is ever going to go through, and I think other 100t owners might appreciate buying their vintage tube set from someone who actually owns and uses the same amp, and doesn't just sell and price based on test results etc.

Cheers.

Verify all you please, but I'm not guessing about any of that. V1 is the first gain stage for both channels, and is in the bright circuit of the vintage channel. V2 is the overdrive tube in the active channel.