Guyatone (toyo sound) GA-440 reverb tank in need of repair...

[kevtronic]

"Dual package" as in one triode to drive and another to recover, or paralleling the triodes for more current drive?

I was thinking more along the lines of triode/pentode dual package like the 6mb8 or a 6GH8A as shown here: Channel Road Amplification: Transformerless Reverb Driver.
But, I see that in the RCA handbook the 6GH8A is showing 200,000 ohms plate resistance verses 20,000 for the 6BM8 (listed for class A amplifier).
Not to mention the plate current is a wee bit higher on the 6BM8 too...
Which, actually the 6GH8A is cheaper in cost, so, that could be a good thing.
Long story short I think for a first timer at this like me I'd be best off sticking with tube closer in specs to the article or just simply use a 6GH8A (they're cheap enough).

The article above uses a 600 ohm input long tank, but I am hoping to use a 800 ohm input short tank, as I haven't yet found an 600 ohm short tank.

Still on a learning curve, but I think things are starting to come into focus.
I love learning/teaching/instruction so don't be afraid to chime in, please correct when needed, as I am for sure not the 'pro you know' on reverb/tank circuits.
There's a big difference between repair/service/mod and engineering, know what I mean - lol...

[Leo_Gnardo]

Wouldn't expect much diff between a 600 and 800 ohm input - driving it straight off a tube plate means you're far from a good impedance match anyway. It's just the expedient thing to do, and it can sound good, as many old Ampeg owners will attest. The quality will have more to do with the tank than what's driving it. No worry about having to use short tank either. I've opted for shorties in some amps that would take a full size tank; whichever sounds better, is the one I install. And just about anything's better than a one-spring tank!

[kevtronic]

Wouldn't expect much diff between a 600 and 800 ohm input - driving it straight off a tube plate means you're far from a good impedance match anyway. It's just the expedient thing to do, and it can sound good, as many old Ampeg owners will attest. The quality will have more to do with the tank than what's driving it. No worry about having to use short tank either. I've opted for shorties in some amps that would take a full size tank; whichever sounds better, is the one I install. And just about anything's better than a one-spring tank!

Well then, based on what you've said I think I'll order this tank and tube and see how it goes:
https://www.tubesandmore.com/products/P-RMOD-8EB2C1B
https://www.tubesandmore.com/products/T-6GH8A

[Leo_Gnardo]

Well then, based on what you've said I think I'll order this tank and tube and see how it goes:
https://www.tubesandmore.com/products/P-RMOD-8EB2C1B
https://www.tubesandmore.com/products/T-6GH8A

If you haven't yet committed to the 6GH8A I'd say 6BM8's your better bet according to the specs you mentioned. Even though the plate/tank match is miles off, at least it's 10x better with the latter.

[kevtronic]

If you haven't yet committed to the 6GH8A I'd say 6BM8's your better bet according to the specs you mentioned. Even though the plate/tank match is miles off, at least it's 10x better with the latter.

Thanks for the quick response and info. I already have a 6BM8 mullard on hand, so what I can do is get the 6GHB while ordering the tank and then we'll have both tubes to apply if need be. The tubes won't go to waste even if I don't use them on this specific project...

[kevtronic]

All the parts are in except for the 1uf electrolytic cap. I have 20 and 22 uf caps for testing of the circuit; if I get that far before the 1uf caps come in. I will start working on putting things together within the next couple of days...

[J M Fahey]

Try this:

both ends are the same, you need 2 buzzer disks and the spring may be the same.

[kevtronic]

Try this... both ends are the same, you need 2 buzzer disks and the spring may be the same.

Thanks for the response and info.
Is this a something you used in an amp to replace the tube driven ceramic piezo tank?
If so did you find it to be a direct replacement?
Any chance you may have some sound takes?

I'm on two bunny trails now.
Not only am I going to continue down the trail of tube driven reverb tanks, but...
Now I am going to be looking at piezo disc reverb tanks too - lol.
I'll have to see if the local RadioShack carries them...
Thanks again...

Edit: "Well, I had a piezo disc laying around from a few years back, so I hooked it up to the reverb input of the amp. I didn't get a significant amount of vibration and/or sound, but I did get some. So, I will be obsessed with this for a while, too - lol..."

[kevtronic]

I got the amp wired back up and everything is working. The reverb sounds nice (at least too me). Hopefully sometime in the near future I will have some info, pictures, and sound clips up...

Stay tuned...

P.S. - I have a bunch of piezo discs on the way, lol, can't help myself - I just gotta make some diy piezo reverb tanks...

[kevtronic]

Guyatone (toyo sound) GA-440 reverb tank in need of repair (added schematic)

I finally got around to making up a schematic for my reverb tweak: GuyaTone 440s (kevtronic).pdf

Seems to work well and the few people who have played the amp say it sounds great.

Hope this helps someone out...

[nickb]

A couple of suggestions:

The reverb tank type is not specified
It would be helpful to highlight the changes.
Look like you dropped in a new PT as the original had a half wave rectifier. Specs?

[kevtronic]

A couple of suggestions:
The reverb tank type is not specified
It would be helpful to highlight the changes.
Look like you dropped in a new PT as the original had a half wave rectifier. Specs?

Good point on the reverb tank specs; it didn't even cross my mind to add it. I'll take a look at the tank and add it to the schematic I made. I never did find a G440S schematic. I was using a G430 that was close to the G440s. The G430 schematic showed half wave rectification, but the G440S amp had full wave when I got it. I'm also using the original PT that came with the G440s. It looked stocked and untouched, but you never know I guess without another G440S or the correct schematic. I've got a pretty good pile of documentation, notes, etc, from the project, so, I'll see if I can't highlight the some of the changes...

Thanks for the watchful eye and tips...

[kevtronic]

The reverb tank I used is a MOD 8EB2C1B that I got from TubesAndMore.com

[DDHopkins]

I recently repaired the same reverb tank in my Teisco Checkmate 88 Solid State Amp. Do you know anything about who manufactured the tank? How about the phono cartridges? Any information would be helpful. Thanks! David

[kevtronic]

I recently repaired the same reverb tank in my Teisco Checkmate 88 Solid State Amp. Do you know anything about who manufactured the tank? How about the phono cartridges? Any information would be helpful. Thanks! David

Unfortunately I don't have any information on the original piezo reverb tank manufacturer, etc. I can say the replacement reverb circuit mod in this thread worked worked well.