New Thunder 1 Reverb Owner

Archer993

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I picked up a Thunder 1 Reverb on eBay to go with my Starfire. Unfortunately the amp arrived not working—not as the seller described. Static, popping swelling sounds. One issue might be damaged tubes as the amp was poorly packed and sliding around the box. I also expect some of the caps might also be leaking.
The secondary issue is that the reverb speaker makes a horrible pulsating hum sound that gets louder if the reverb pot is turned up.
I know schematics for this amp have been discussed here but I haven't been able to locate one.
Can anyone point me to a diagram so I can get going on repairs?
Thanks in advance...
 
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Hi Archer and Welcome to LTG!

Unfortunately, we gave our best amp guy, Cap'n Juan, the day off. :( The good news is he's scheduled to clock in at first light, tomorrow. He can get you fixed up. Just look for a gringo with a wide sombrero and suitcase full of Coronas. :D :D

~nw

ps, you might have to furnish the limes.
 

capnjuan

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Hola Archer y bienvenido a LTG! I'm logging in from a cantina with wi-fi just outside of Sonora ... the damn Federalis were on my tail all night ....

Congratulations on your amp; yes ... it might be the tubes but ... but that's usually too easy ... they are tougher than most people give them credit for ... but that's no reason not to start looking around for replacements.

Before I forget, hit the PM button at the bottom of my post and send me your email address ... I'll send you a schematic - and/or - you can work with this on-line copy of the T1 RVT schematic. It's easier to read on-line than it is down-loaded but whatever works best for you.

The T1 RVT uses two multi-section can caps; in addition to one loose section, one 4-section can cap for the primary filtering and a 3-section can cap for the reverb amp. 3-section caps are still around, 4-section caps ... no longer in production ... work-arounds will be necessary.

Static and popping are common with corroded tube sockets and tube pins and dirty controls and mechanical connections. You need to get some De-Oxit or equal, spray the sockets, and push/pull the tubes several times to clean off the grunge. While you're at it, clean the controls; squirting cleaner inside the body of the pots and spinning the knobs back and forth several times. Do the same for the power switch and disconnect the reverb can and clean the RCA jacks and plugs; same thing ... get them wet, push on / pull off several times.

The 'pulsing' is likely one or more sections of the reverb can cap leaking; no point in changing it and not doing the primary at the same time. Good luck with your amp and welcome to LTG!
 

Archer993

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Thanks very much for the information. I did do all the socket and switch cleaning and changed out the preamp tubes with some success. I have ordered supplies and should start really digging in later this week. Actually Antique Electronics supply does have some 4 section can caps so I ordered a beefier 50/50/50/50 but the 60/40/40 is a no go and I will make my own external cap can using Sprague Atoms. What's with all the 32uf caps? Oddballs.

I am a bit worried about the reverb as the unit looks rigged—there is no plug in the jack near the resistor/cap board, instead a wire passes directly through the jack and is soldered to the jack lug. It also looks like an unskilled chimp did the soldering to the speaker terminal and not a Hoboken tech.

What really strikes me about this amp is the attention to aesthetics. The color coordination between the tolex, grill cloth, handle, and cords is usually not found in an amp. Pretty cool!
 

capnjuan

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Hi Archer: glad you found suitable can caps; sometimes they're out there ... sometimes not. I suggest you substitute Sprague Atom 25uf/25V caps for the 32uf - no difference in either tube bias or frequency response.

Pictures would help here ... not sure what you mean by "...resistor/cap board ...": do you mean the reverb amp circuit board at the opposite end from the PT? Directions here for posting pics on LTG. You need an on-line photo hosting account. Upload the pics there, acquire the IMG address, and paste it into your draft post; the BB software, following the IMG address, will go out and find the pic and display it.

Whatever you have in the way of crappy wiring probably wasn't done in Hoboken. Looking forward to the pics.
 

capnjuan

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Thanks Nigel; feeling much better ... thanks for the refreshments ... :D
 

Archer993

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Ah, the old "Coronas in an ice bucket" ploy. Works every time. I enjoyed mucho Dos Equis in an ice bucket several years ago while working on Troy on the Baja. Just remember, wipe those bottle necks dry or amp trouble will seem like childs' play compared to your plumbing problems!!!!
 

capnjuan

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Archer993 said:
... several years ago while working on Troy on the Baja. ...
Troy on the Baja? Hi Tim; if you've already done the cleanup ... not telling you anything you don't already know but I think the next stop is the preamp cathode caps and resistors. Still having a hard time visualizing your reverb return condition.

The reverb supply is taken from the + terminal on the 12" speaker, through a cap and resistor in series, then into the reverb can. The output comes back via a cable; RCA plug at the can end, through a chassis grommet, and hard-wired (I think?) on a terminal strip n/ the reverb amp.

Does you amp have an exposed metal backpanel to the chassis (version II) or do they protect the electronics with a plywood panel (version I)? Black or beige tolex? Is your amp cathode- or fixed-bias? Some of the earliest makes are cathode-bias. Our member Zulu's is cathode-biased and the 12AX7 and 6BM8 reverb tubes are hard-wired at tube sockets in the chassis.

There are a few other T1 oddballs floating around ... here's a bias 'belts and suspenders' model; has a bias supply to provide a negative voltage to the grid and a cathode resistor w/ a bypass cap to push up a voltage on the cathode:

GuildT1belts.jpg


Good luck with yours ... looking forward to some pics.
 

Archer993

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Will have to get up to speed on an image hosting service.

The movie Troy was filmed mostly outside of Cabo.

Thanks for that last pic - will post mine soon.

100_0033.jpg
 

capnjuan

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We've seen fewer of these version 2s than the earlier model; just small differences in the electronics ... the big changes were cosmetic ... but the 'star' ground is new and the loose brown ps filter cap moved from the gap between the transformer and rectifier to its current location which was formerly occupied by a wiring strip.

Looking forward to more chassis shots especially the reverb return wiring; looks pretty clean!
 

Archer993

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Some better innards shots. A few caps changed by me as I had these on hand.

innards5.jpg


innards4.jpg


innards3.jpg


innards2.jpg


innards1.jpg
 

Archer993

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The cap in the photo came off the reverb circuit board. It's supposed to be 50uf!

badcap.jpg


Here's the "wire through the jack" shot. The soldering inside was sloppy and oe wire was hanging by a thread.

reverb1.jpg


reverb2.jpg


The guarantee and speaker code:

labels.jpg


The baffle and a curious circular trace as if this is scrap wood. I may replace it with some birch ply.

thebackbox.jpg
 

capnjuan

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Hi Tim: I'm working on getting you a cleaner schematic ... part of what's below taken from what I think will work ... anyway ... the reverb input at the reverb amp ... If that white wire hits the junction of the .0047 cap and the 33K R, then all that's left if confirming that the other end of that bare wire is connected to the ground side of the RCA jack at the can ... can ground ... If so, I think all that's left is splice something on to take it to chassis ground. Also, the heater wiring for the 12AX7 looks out of place ... underneath on earlier models; no pics of later ones like yours.

GuildArcher04.jpg


The R/C mess at the reverb can input ... that's ugly. The R is 'vintage' Guild; again, on the earlier models, the R and C were mounted on a small board that was fastened up higher using one of the 12" speaker hold-down nuts. I don't know if it sitting on the edge of the reverb can is another engineering change or not. The 'thru wiring' looks nasty but if the location is factory, then they'd be stuck coming up with a short length of cable with an RCA plug on one edge ... somebody might have decided .... you know what I mean.

V1 v. V2; you have a plywood cab ... the earlier version had particleboard ... make that godawful particleboard; absorbs moisture, slowly disintegrates, and doesn't withstand point loads. No explanation for the paint arc on the baffle but it's the same material as V1.

12" speaker: code 486-704 or 466-704 ... I can't find it; is there another set of codes on it? Originally sold with CTS 137XXX like the 8" which is original.
 

zulu

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Looks mighty familiar. I have a clean schematic the friendly and esteemed Coastie sent. Let me know if a high res photo of it would help.
 

capnjuan

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Hi Tim: the crummy-looking solder job on the 12" speaker terminals happened after the original was changed out ... don't know if that's when the R and C got relocated to the can or not ... if it was relocated at all. Provided you have continuity from the outside to the reverb can transducers, it ought to work ... assuming the transducers still work.

Accutronics acquired all of the Hammond / Gibbs patents and designs. These days, Accutronics won't work with you if all you have is an old 4-digit #; just guessing, too many cans moved from one amp to another ... Accutronics can't/won't be sure if that can was originally sold with that amp or not.

If after testing, you think yours needs to be replaced, we can try to confirm an Accutronics spec that will work; Coastie's had a 4FB3D1B; 1.475K input impedance, 2.250K output impedance ... but ... and see remark about Accutronics above, the can was 'volunteered' in there by a friend who worked on the amp. In retrospect, I think a 4ABXXXX might work better ... 8 ohm input impedance matching the impedance of the source ... the 12" speaker.

@Zulu: Hi Z-man ... all is good?

Edits: a couple of syntax errors and language/Accutronics spec #s.
 
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