Designing a stereo tube guitar amp

[R.G.]

Anyway, this is classic trolling. Stop rising to the bait, RG.

But Steve, this is one of the only pleasures left to an old man. 8-)

[The Dude]

Here's a stereo guitar amp from 1961. You can see that the PT and two OTs are in the bottom chassis on the floor of the amp with two PIs. It has a two channel preamp (A&B) in the top chassis. You can select stereo, A, B, AB. Plugging a guitar into channel A with the selector switch on stereo powers up one OT and one speaker. With the selector switch on A, you get two OTs and two speakers with double power.

Do you have any more info on that amp- Make/Model?

[jazbo8]

Here is a well documented stereo guitar amp project at Hoffman's:

Preamp
Power Amp

I would mate it to a pair of 2x12 cabinets, will sound pretty awesome...

[NZaudio]

I have a request from someone to build a stereo tube guitar amp head. Probably around 15 watts X 15 watts using el 84's.
This amp will have quite a few bells and whistles. (chanel switching on each channel) effects loops and so forth. It will be quite an amp as it will have 2 of them in one.
I realize that the more complicated the amp, the more that potential problems are compounded in the design. Hums oscillations and so forth. One thing I am particularly concerned about is the transformer placement. For example amp 1 will be on the left and amp 2 on the right of the chassis. Lets just say that the input for amp 1 will be on the left side followed by the tone stack and then the second amp input will be basically starting in the middle of the chassis followed by it's tone stack and so forth.
I was thinking of having 2 power trannys and 2 OT's.
The power tranny for amp number 1 will be basically in the middle of the chassis away from it's input but then the problem will be that it is close to the input of the second amp. Being that the power trannys will be completely mounted on the top of the chassis, will that still possibly effect the input of the second amp?
One factor would also be the size of the chassis as although I don't want a huge chassis it would have to be big enough to work properly considering the above problems mentioned.
I hope you can understand where I am coming from.
Thanks for reading the long post.

Disregarding the speaker side of it, if it would be a combo amp, that would be useless as a stereo amp but otherwise...WHY NOT? Go for it John and always think that there are heeps of HiFi amps out there, lots of them in stereo. They only look a bit different but basically it's the same. What's good enough for HiFi is good enough for stage. I also would go for a good DC powered preamp part to get the thing nice and quiet. Valves do not really hum and make noises, it's all about the proper design work you put into it.
Heeps of good old books out there if you get stuck, dating from 1940 on but not much has really changed.Good Luck with your project.

[Chuck H]

Long dead thread, but:

The "stereo" amp I was asked to make was partly intended to allow for two volume levels of power tube clipping. If Johns customer had any similar ideas things get more delicate. What's good for hi fi is good for stage only goes so far. A guitar amp isn't just a reference amplifier. Having preamp overdive (channel switching) included in the design AND having two preamps like this AND two power amps AND being able to clip the power (as any guitar amp should) AND a tube reverb AND putting it into a single compact package AND keeping it stable is just unreasonable for a guitar amp. For a hi fi amp where the signal is never intended to clip anywhere and there are generous amounts of local and global feedback employed, maintaining stability with extra features is EMINENTLY more possible. JM2C on that matter.

Something I use to do, and would work instead of a single stereo combo, was to use two fifteen watt combos. Both with effects loops. I had the effects loops wired with A/B switches so that I could choose which preamp was in use and whether that preamp ran through the effects buss and whether it fed one or both power amps. Using a mono to stereo effects processor I could also achieve stereo effects from either preamp. Easy peezy. Both combos had reverb so I could choose separate reverb levels for either channel. And another nice thing about doing it like this is being able to take only one amp for small gigs instead of always having to take one big amp. Also, when both amps are employed you can place them on opposite ends of the stage for audible stereo separation. I eventually got tired of the novelty and now just play through a single amp again. As I think most players would.

[Diablo]

Do you have any more info on that amp- Make/Model?

Hello Dude.
The amp has a Capitol badge, and no model information. I believe it was built by Lectrolab (Sound Projects in Cicero IL) in 1961, based on the transformer (Transco) and speaker (two Jensen C12Rs) manufacturing dates. I've never found or seen another like it on the web. It has four 7591 tubes, cathode biased, and five 6EU7 tubes, and a GZ34 rectifier, 450 volts on the plates. Controls are volume, tone, tremolo intensity and speed, and bright switches. The amp has a lot of sag and compression because of the voltage drop across the screen supply resistors. I haven't found a schematic, and I haven't taken the time to trace out the circuit and draw it up. I brought it back from the dead, and probably saved it from the landfill. This thing really puts out some great tone and I can't see me ever selling it.

[The Dude]

Hello Dude.
The amp has a Capitol badge, and no model information. I believe it was built by Lectrolab (Sound Projects in Cicero IL) in 1961, based on the transformer (Transco) and speaker (two Jensen C12Rs) manufacturing dates. I've never found or seen another like it on the web. It has four 7591 tubes, cathode biased, and five 6EU7 tubes, and a GZ34 rectifier, 450 volts on the plates. Controls are volume, tone, tremolo intensity and speed, and bright switches. The amp has a lot of sag and compression because of the voltage drop across the screen supply resistors. I haven't found a schematic, and I haven't taken the time to trace out the circuit and draw it up. I brought it back from the dead, and probably saved it from the landfill. This thing really puts out some great tone and I can't see me ever selling it.

Thanks! Info much appreciated! I'd love to find one of these.

[Diablo]

Thanks! Info much appreciated! I'd love to find one of these.

Here's a link to more pics:

1961 Capitol Guitar Amp - Album - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
Capitol Amp Large Photos - Album - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

I forgot it has two phase inverters, so that makes six 6EU7 tubes.

[cooldude666]

stereo is common in hifi. look that way for inspiration. this is sort of uncommon in guitar but in hifi/stereo(eh?!) systems it's common.

[walkman]

This might be of interest to stereo guitar amp builders

The Goldentone Soloist series 6x6 stereo guitar amplifier, made by Rose Morris



1760 “Soloist” series 1962 - 63 30 watt “Stereo” amplifier. Two 15 watt amplifiers with 6 x 6 inch speakers Temolo only.
1761 “Soloist” series 1962 - 63 30 watt “Stereo” amplifier. Two 15 watt amplifiers with 6 x 6 inch speakers Tremolo and reverb

Please visit Neale Amplifiers Guitar amplifier, restoration projects, Goldentone

also seeDerek Lark Songs | ReverbNation for an audio demo

[Gingertube]

This might be of interest to stereo guitar amp builders

The Goldentone Soloist series 6x6 stereo guitar amplifier, made by Rose Morris

[ATTACH=CONFIG]26226[/ATTACH]


1760 “Soloist” series 1962 - 63 30 watt “Stereo” amplifier. Two 15 watt amplifiers with 6 x 6 inch speakers Temolo only.
1761 “Soloist” series 1962 - 63 30 watt “Stereo” amplifier. Two 15 watt amplifiers with 6 x 6 inch speakers Tremolo and reverb

Please visit Neale Amplifiers Guitar amplifier, restoration projects, Goldentone

also seeDerek Lark Songs | ReverbNation for an audio demo

Rose Morris were great copiers - in this case what was copied is an AMPEG Echotwin

To take advantage of a stero setup then make use of what has been done for you - consider using one of the BTSE Modules here: ::::::::: Accu Bell Sound Inc :::::::::

Cheers,
Ian

[Chuck H]

If a mono amp has an effects loop you can set up any stereo effect to send "R" to the loop and "L" to something like, say, a 20W Yamaha SS amp from 1997 that you bought for a hundred bucks. BAM! stereo effects on stage.