Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #117928  by BJolley
 Sun Aug 26, 2012 10:28 pm
Looking for advice from those with more expertise. I have a mid-1980's Seymour Duncan Convertible 60 watt tube amp like this:

I purchased it used in 1997. In the last year or so the preamp quit working -- so plugging into the input jack provides no sound. The amp has an effects loop on it and if I plug directly into the effects return jack -- bypassing the preamp -- I do get plenty of sound but none of the vol, tone, OD, of the preamp. To avoid this amp becoming a large paper weight I am considering adding the Boss FDR-1 Fender Deluxe Reverb modeled pedal to act as the preamp. My hope would be to salvage the remaining operational components of the amp while at the same time gaining some Fender -- and in turn Jerry -- tone. I am merely a hobbyist/bedroom player. My questions are:

1. Does anyone have experience running directly into an effects return jack to bypass the preamp and go directly to the power amp? and
2. Any thoughts on the Boss FDR-1? It seems to get pretty good reviews online.

Thanks for any input.
 #117929  by gpilcher2001
 Sun Aug 26, 2012 11:23 pm
Have you tried re-tubing the amp? It could be as simple as a bad pre amp tube. If you have output and no funny smells or noise the amps probably fine. I Would go to guitar center ( for convenience) and get as many of the small tubes that your amp uses and replace those first. It could probably use a new pair of the bigger tubes but you'll have to have them biased by an amp tech. The small ones you can do yourself. Just make sure the pins line up with the socket. Easy as changing a light bulb

The boss pedal is a pre amp in a pedal. It should work just fine using it in the effects loop return. If you already own the pedal the manual should explain how to do that. If you want to check it out before you buy the manual is available @

As old as that amp is it's probably never been re-tubed. Which means your big tubes (known as power tubes) probably don't have much life left to them. It will probably cost you 200 bucks, including the bias from the tech, to re-tube the amp. It just depends on how many tubes you need. You will need to buy the power tubes in matched sets and type, re: 6L6 or EL34. If this is all you need to get the amp running again you will be surprised how good the amp will sound. Tube amps need a little maintenance. If your just a bedroom player. A new set of tubes will last a long time.

Lastly if the re-tube doesn't fix your problem then the amp has bigger problems and will eventually completely fail. So keep that in mind. If the re-tube fixes the amp and you like it with the boss pedal all you have to do pull the little tubes out and save them until you want to use the pre on the amp. I hope this helps
 #117946  by BJolley
 Mon Aug 27, 2012 10:20 am
Thanks for the input. I actually had a very skilled amp wizard work on the amp. He tested all five tubes, checked input jack, etc. He ultimately concluded one or more of the transistors in circuit board has failed. The parts are out of production and nearly impossible to obtain. Thus, I came up with the idea of adding a preamp pedal to bypass and replace the failed circuit. Started looking at EQ pedals and then found the FDR-1. Since I, like most Jerry enthusiasts favor Fender tone, I thought this might be a feasible alternative to scrapping the amp.