Thunderstar Combo - No Reverb

Hi All

I am working on a Thunderstar combo, and I have everything working except the reverb. Just bought a NOS 6GW8 tube for it, but still no workee.

I have checked all the components that I know how to (there's resistance at the input and output of the tank, and I have tried a couple different tanks) in the reverb circuit, which brings me to the wacky transformer in the input circuit. How do I test it?

By the way, when the reverb is switched on, I can shake the tank and get a "crash". Here's the schem:

http://www.mediafire.com/view/8hj09ur3x5ld92n/Guild_Thunderstar_Lead_Amplifier.pdf

Thanks In Advance

earache

Not sure what to tell you. There are more qualified people to respond than me. But I have the same amp. When I first bought it, it seemed the reverb wasn't working. The prior owner told me "sometimes you just have to let it warm up and honestly just bang on the side a little and it comes on". And I found...essentially that was the case.

if you are hearing the "crash" when it's on, to me that means it's working. Or mostly working. Maybe if it has been sitting dormant you just need to let it warm up a few times and really play with the reverb pot and such. (And bang on the side a little?). Let it warm up for about a half hour or more a few times and see what happens?

I have a tech working on my T-Star as we speak. Here's his report on the reverb, if this helps any.

The reverb is kinda weird. Doesn't sound like a Fender reverb, and the level control does weird things to the main level.
If you turn it up all the way, after a while it gets a mechanical feedback thing going. Weird.
I did some checking, there are several off value resistors in the mixer circuit, they are the likely cause of the level weirdness.
(The mixer circuit is where all the channels come together to be fed to the power amp. I count the reverb circuit as a channel in this case.
If you look at the schematic, it'll make more sense.

Click to expand...

if you can hear a crash when you hit the tank then your problem is definitely on the input side, so that simplifies things.

so yes, the wacky transformer could be the problem. You need to see what it's outputting and make sure you are using the right tank to match it. Reverb tanks come in wildly different input impedances ranging from 8Ω to 1475Ω. Output impedances are similarly variable but at least you are getting sound.

Do you have the original tank to the amp? on that is a six digit (if i remember right) code that tells you the input and output impedance amongst other things. They still use the same code today so you can toddle over to the Accutronics site and check it.

If you can see what impedance it's supposed to be, that should tell you what your transformer should be outputting to match it. Now, for how to work that out you'll need to talk to someone better than me. I suggest one of the DIY amp forums.

Anybody know of a replacement for the reverb transformer?

Make a search on this page:

http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_misc.htm

for this: GUILD-THUN-RT

This is the transformer that I used to replace mine.

Jack

Hey 59panhead - that's exactly what I did and the transfo is being wound perhaps even as we speak! Thanks for you input