NAD

[Nuuska]

Howdy

About two months ago I spotted a For Sale ad w GUILD Thunder 1 REVERB amp. I knew the seller by name - we have many common friends - but never met.
I had no extra loose money at the moment. He agreed to my proposition that I send him 50€ now - rest when I can - after full payment we organize transport.
He had good enough pictures and told the reverb is not working.

Today someone was passing by and delivered it. I removed the back panels to inspect some before connecting power.




The wiring to 12-inch Fender speaker was . . . err . . . questionable - so I removed the speaker to enable the original cable reach. While speaker was off - I noticed the hole was not factory made - perhaps someone had a trained beaver to chop off - same thing was w the reverb speaker. I vacumed the dust off Fender and discovered a rip in the cone - put some glue on it plus on a punched spot. Since Fender is not original - I'm finally going to use one nice speaker, that I have had on a shelve for years. It is Electro-Voice Wolverine - the older one w three rounded supports instead the later 4 edgy ones.










The glue is fresh on the picture - it will turn almost transparent when dry. Regular wood glue.

Next attention to reverb speaker - cable was not attached - but fortunately inside the cabin - so I soldered it. The speaker has had some water damage and/or other mechanical brutality - as you can see looking at the cone. No idea if it is the original speaker.






I have one nice old Jensen in ship shape - unfortunately it overlaps the Fender - but since the front panel is home/beaver-made anyway - and of chipboard. . . - I might just cut a new baffle of birch plywood - the scandinavian quality w 1mm layers - that is 12 layers for 1/2 inch panel. If I move both speakers just a tad closer to their corners they should fit in. That is a job for end of summer or fall. Meanwhile them both speakers will do.





While doing all this I saw the obvious reason for the reverb not working - there was no wire from 12-inch-speaker to that resistor w capacitor that is on the cabinet left in second picture. I did not worry about it - There is the tank - I've not measured that yet - but tapping on it does not provide any signal to reverb speaker - nor is there any signal if I remove that return cable from tank and try to feed something there. The reverb amp might be faulty. And finally I get to the bonus of this deal : Seller had not mentioned - but the amp came w original GUILD pedal - hardwired, so not easy to loose. The pedal produces a click when REVERB pot is turned loud.



I do have a schematic for this amp - hope there are not too many different variations of it.

All in all I'll have some hours work ahead when the time comes. Meanwhile I enjoy what I got : The sound is VERY pleasant - Tremolo is nice - although producing some "popping" when no signal is there.

For 300€ - deliverd - I'm very happy.

 

[GGJaguar]

Nice amp, congrats! The speaker driven reverb is really cool!

 

[hearth_man]

That's a great project. These rescues are worth the time. You'll have a nice amp when your finished. Keep us posted.

 

[mavuser]

very cool, she's in the right hands now.
pretty sure that was the original reverb speaker (CTS, 50th week of 1964)

 

[Nuuska]

Back from lake - rebuilding the dock in 80F in shadow - dock in direct sunlight - pheww . . .

Had a quick look at the reverb tank. Both coils work - both springs are there. Then looking at the schematics one obvious reason for it not working shows there. The input uses the speaker hot signal decoupled w series capacitor and dampened w series resistor. The input ground has no wire coming to it. When tank is new and the RCA connectors are riveted to it - there is a nearly 0 ohm connection between input and output grounds. But as decades go by ( wenn Jahrzähnten einkaufen gehen . . . ) the rivet connection oxidizes and finally there may be no connection at all.

I soldered a wire inside the tank between ground lugs. Next I may have to replace the cables - or at least put new RCA-connectors on them.








Then studying the schematics a bit more - I discovered, that when reverb is OFF the direct sound comes via that amp & speaker, too. This explains the "POP" when switching. On preamp the signal is deriver from anode - decoupled w capacitor - BUT NO PATH TO GROUND. On reverb amp the switch is after spring-return preamp. There the signal gets picked up from a point that is connected to ground via resistor. My solution will be to add about 2MOhm grounding resistor to that cathode circuit.

While the direct sound comes through both speakers when reverb is switched OFF - that leaves the non-functional reverb to reverb-preamp section.

In my imagination it is almost done - just have to get a round TUIT

And when I eventually replace the baffle - I may put some other grillclothe there. I have somewhere 2old Marshall grills - Not sure if they're large enough

 

[Soul Tramp]

So, what happens when you hit 88db and the Flux capacitor kicks in?

 

[Nuuska]

I have not tested the amp at loud volumes - for two reasons :

- there are two other persons in the house - summer holiday.
- I never play w that kind of volume anyway.

But once I have all set up - I'll take it to rehearsal of the band I've been mixing for18 years and let the guitar player have a rip.

 

[Bill Ashton]

I can only add the following: both speakers originally would have been CTS-built square-magnet style, so the 8" reverb
speaker is original, the Fender speaker not...but you probably already know that! The footswitch I would also say is original.

When I was in high school, ~1970, I bought a Thunder 1 that had belonged to a local player, but the second owner had
butchered a repair; I used it as an additional speaker cabinet for a while. I remember thinking what a world of difference
in its build between my '63 66-J and this POS...

I don't know whatever happened to it, but no remains were found when we cleaned out my parent's home for sale in 2015; I suspect my father may have parted it out in flea markets, if it remained at all...

Sorry, not really helpful...

EDIT: If I remember correctly, this was supposedly like a Princeton Reverb power wise, although using the rather odd-ball output tubes; of course, we did not know that way back when...@Default is likely a good source of into.