Modded Fender Bassman 135 - Value?

[gimp]

Found a Bassman 135 on the local Craigslist, and it has been modded a good bit. The seller is asking $299 firm - thoughts?

Up for sale is a Fender Bassman 135 amplifier for $299 -- this particular amplifier is extremely flexible, quite unusual, and very interesting, with shrewd modifications that make it an extremely powerful and versatile piece of equipment outfitted with the unmistakable sound of four 6550 power tubes. It is MUCH louder than a stock Bassman 135 -- we're talking MAJOR power here.

It is completely analog, point to point wiring, but with all the excessive and unnecessary circuitry removed -- no Normal Channel; no Master Volume. What remains is a stripped down, lean, mean power machine.

The controls are basic: just Volume, Treble, Midrange, and Bass. There's also a "slope" control that shifts the bass frequencies up or down so you can dial in the ideal setting for each room -- lots of glass, stone or other reflective surfaces?...lower the effective range so you can get those fat low notes -- playing in a "boomy" area?...raise the slope to get the bass response up high enough to avoid the room's resonant frequencies.

You can see in one of the photos that the Bass Channel is operational and the Normal channel has been taken completely out of the circuit, electronics removed and holes plugged for a nice, tidy appearance. The Master Volume is out of the circuit as well -- why a Bass player would need a Master Volume remains a mystery, but anyway, it's gone.

The design couldn't be simpler -- if you look at the photo that shows the open back, you'll see the four enormous 6550 power tubes, plus a 12AX7 to drive them and another 12AX7 for the pre-amp. That's it...! CBS built regulators and governors into the circuit to prevent the amp from blowing the low-wattage speakers they were using, and thus reduce the cost of warranty repairs -- all of that is gone, thankfully!

Behind the power tubes you can see the massive output transformer that accounts for the raw power that this amp exhibits and is also responsible for the weight -- it's heavy, just as you would expect an amp from from this era to be! This ain't no Rumble Bass or Hartke combo -- this is for big boys only...!

The sale also includes a custom-made after-market padded cover made by Tuki (also in the photos).

[kbakerde]

Originally Posted by gimp

Found a Bassman 135 on the local Craigslist, and it has been modded a good bit. The seller is asking $299 firm - thoughts?

Well, I just paid $500 for a Bassman 135 head and Matching Cabinet, so IMHO the price is in the right ballpark.

The mods are a problem for me, I just am not sure I like that someone took out the "excessive wiring" out of a fairly complex piece of electronics. I have heard of others modding the 135 to use the 6550's to increase the power and headroom. But the biggest concern is the removal of the master volume. For one, I thought it was pretty integral to the design of this kind of tube amp, and second, I find it really useful.

If you want it, I would try to talk him down. Work your way to $250. I think the mods detract more than add, in part due to the fact there isn't a schematic now for this unit. I also would not part cash unless the seller allows you to take it to a local good amp tech to be looked over.

[gimp]

I agree that the mods detract. I really don't get the lack of a master volume. You are just confirming what I was thinking. Honestly, I wouldn't pay more than $200, but I'm sure I won't hear anything back on an offer like that.

[BassmanPaul]

i wouldn't touch it with a barge pole! 6550's increased heater power drain alone is going to be stressful for the power transformer. Regulators and governors??? The ad makes little sense!!

Edit: The schematic is readily available with a Google search.

[kbakerde]

Originally Posted by gimp

I agree that the mods detract. I really don't get the lack of a master volume. You are just confirming what I was thinking. Honestly, I wouldn't pay more than $200, but I'm sure I won't hear anything back on an offer like that.

Yeah, my first thought was to offer $200, thinking it would ultimately end up at $250, or you might get told to go to hell!!

BUT, again I just bought one, and I really like it's sound so keep your eyes peeled, cause there is a slowly increasing number of us loving and using the SF Bassman 100/135 heads.

[kbakerde]

Originally Posted by BassmanPaul

i wouldn't touch it with a barge pole! 6550 increased power drain alone is going to be stressful for the power transformer. Regulators and governors??? The ad makes little sense!!

+100

So I know my way around wiring a cabinet, I can wire any kind of guitar you want, but I piss my pants thinking about monkeying around in an amp. Once this thing breaks, it will cost a fortune as again, there is no schematic for it.

But that is just my opinion, but it feels good that a guy who actually KNOWS about working on tube amps thinks it's a bad idea too.

[gimp]

Part of me was factoring in the cost of "fixing" the mods if I bought it. I'm not sure I'd be ahead at a $200 offer!

[will33]

No doubt it needs to be looked at by a tech prior to sale. That would involve a bench fee, you 2 can deal with how that figures in price.

That said, the 135 isn't like an old blackface. Doesn't really have any vintage/collector value. I paid $325 for mine and put another $160 worth of work in it. Those mods sound like something I might quite like, assuming they were done correctly, reliably, etc., thus the bench fee. I've often thought of jumping the channels together on mine internally and freeing up the knobs on the normal side for stuff like reverb and/or a built in dirt pedal type effect. Being able to raise the frequency of the bass knob or change it's slope is an improvement, IMO. More power never hurts either.

At $299 I'd be inclined to pick it up, but that's just me.

[kbakerde]

Originally Posted by will33

No doubt it needs to be looked at by a tech prior to sale. That would involve a bench fee, you 2 can deal with how that figures in price.

That said, the 135 isn't like an old blackface. Doesn't really have any vintage/collector value. I paid $325 for mine and put another $160 worth of work in it. Those mods sound like something I might quite like, assuming they were done correctly, reliably, etc., thus the bench fee. I've often thought of jumping the channels together on mine internally and freeing up the knobs on the normal side for stuff like reverb and/or a built in dirt pedal type effect. Being able to raise the frequency of the bass knob or change it's slope is an improvement, IMO. More power never hurts either.

At $299 I'd be inclined to pick it up, but that's just me.

Will, if you wanted to do the Mod to the 6550's right, what all would be involved?

[will33]

Originally Posted by BassmanPaul

i wouldn't touch it with a barge pole! 6550 increased power drain alone is going to be stressful for the power transformer. Regulators and governors??? The ad makes little sense!!

Edit: The schematic is readily available with a Google search.

This^^,

Although without the aid of a tech, OP could at least look in back and verify the original transformers are not in there.

If they are, it's no longer any sort of deal. Walk away.

If it were me, I'd at least still go have a look though, I'm just curious like that.

[taurus1]

if it operates as advertised and needs nothing, I'd be all over it

[will33]

Originally Posted by kbakerde

Will, if you wanted to do the Mod to the 6550's right, what all would be involved?

BassmanPaul would be better qualified to answer, but, transformees at a minimum and those are the most expensive things in the amp.

[BassmanPaul]

Originally Posted by kbakerde

Will, if you wanted to do the Mod to the 6550's right, what all would be involved?

To do it right, a secondary heater transformer should be added to supply the additional demands of the 6550, that's about 0.6A per tube or 2.4A for the quartet.

The gotcha in all this is that you will garner no more usable output from the amp. Being an "upside down" amp the additional heat will reduce the service life of all of the components within the chassis.

[will33]

If anythings going to become a problem it's the power section mods. The bass control mod sounds like it would help as far as being a more effective bass amp. If not, those will be in the preamp....cheap parts to change.

[taurus1]

I had my Traynor YGL3 modded from El-34 to 6550, still has the original transformers, it's an upside down amp, way more power and headroom and no component issues from heat.
I think 135's have a fan anyway, I could be wrong.

[will33]

Good point as well about the heat. It would need at least cooling fans. Mpre preferrably, be built into a custom headcase upside down, so the tubes are on top.

[BassmanPaul]

Originally Posted by taurus1

I had my Traynor YGL3 modded from El-34 to 6550, still has the original transformers, it's an upside down amp, way more power and headroom and no component issues from heat.
I think 135's have a fan anyway, I could be wrong.

Traynor amps use oversized Hammond transformers. They are capable of handling a fair bit more "abuse" than other manufacturers products. Changing from the EL34 (6.3V @ i.5A) to a 6550 (6.3V @ 1.6A) is not such a large change. No matter how you feel, the output will not be much different. The power sent out has to come from the power supply. If left stock then little difference.

[will33]

Originally Posted by taurus1

I had my Traynor YGL3 modded from El-34 to 6550, still has the original transformers, it's an upside down amp, way more power and headroom and no component issues from heat.
I think 135's have a fan anyway, I could be wrong.

The bassman's have no fans, though there's room in the 135 to add a proper, shrouded, maybe even dual fans if they're smaller ones.

The angled faceplate, and of cpurse the labels being upaide down would make it a little goofy to mount flipped over, but would solve the heat thing with a vented top.

Mine needs some work done now, though it performed trouble free for many years, so I sort of view it as a mod platform. Freeing up some pot holes for other add ons. Changing how the bass control works and/or adding some highpass filtering would really help these amps. They waste a lot of power pushing subwoofy stuff, which makes them not sound as loud as other 100 watt tube amps. I think helping it put there would let it run loud enough to use on a lot more gigs than I do, probably while even keeping the 6L6's and not messing with the power section....yet.


As far as the OP's purchase deal, I'm personally just more inclined to take a risk on something like that, just because it might be cool, and I don't have to depend on it as my only gigging amp. If he's looking at this as one amp he needs to depend on all the time, I might steer him towards something that wasn't messed with.

At a bare minimum, I'd at least see that the transformer issues Paul spoke of were good to go. If you don't have to buy transformers, the rest is a lot cheaper risk.

[taurus1]

Originally Posted by BassmanPaul

Traynor amps use oversized Hammond transformers. They are capable of handling a fair bit more "abuse" than other manufacturers products. Changing from the EL34 (6.3V @ i.5A) to a 6550 (6.3V @ 1.6A) is not such a large change. No matter how you feel, the output will not be much different. The power sent out has to come from the power supply. If left stock then little difference.

"not be much different", I don`t agree, it`s a substantial audible difference.
modded amps are a crap shoot no doubt about it, sometimes though you can get a gem that was modded by someone who knows what they`re doing.

[B-string]

IMO he can add whatever spin he wants, he took a Fender Bassman 135 and made it a homebrew amp (homebrews are worth squat).

If brought to me to check out I would ask for schematics of this once production amp and be very tempted to refuse touching it. Any safety testing done on the design is void and I would not want to be responsible for injuries or damage.

BTW Paul some newer 6550's like the Winged "C"'s have typical heater draw increased to 1.9A per valve.