New Thunder 1 Reverb Owner

Archer993

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I think the first course of action will be to replace the cap can for the reverb amp - the sound from the speaker sounds like a 60 cycle mess so something foreign is getting by. After that, I'll start to dissect the rest. Stay tuned . . .
 

capnjuan

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capnjuan said:
... you have a plywood cab ... the earlier version had particleboard ... make that godawful particleboard; absorbs moisture, slowly disintegrates, and doesn't withstand point loads ...
Explaining godawful: Coastie's T1 struck on its right side (when facing) by - probably - one of the forks on a forklift. Because the particleboad doesn't have any grain, it just shattered but not before transmitting the energy all over the place. The right side panel disconnected itself from the top because particleboard cabinets don't have finger-joints .. they have staples and Elmers glue holding them together.

IMG_0902.jpg



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IMG_0905.jpg



My beautiful hand-shaped baffle batten ... :evil:

IMG_0907.jpg



This is why particleboard cabinets bite ... although some people say they suck ... while others say they eat it .. as you can see ... opinions vary but at least Archer's and the later versions got plywood. Go You Guild :p
 

Archer993

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Mine actually looks like it's constructed of planks — I can see very straight grain as with fir. Or, maybe some straight grain pine. Could this be?

From what I've read elsewhere pine, especially old pine, yields the best tone...
 

Archer993

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I'm totally confused by the whole reverb circuit. The green wire is coming off of the regular speaker terminal, not the reverb speaker.
Did someone reverse the black and white wires on the regular speaker.
Could the filter caps, having malfunctioned, fried other components down stream.
So many questions. . . .
 

Archer993

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SPEAKER UPDATE:

465-704
The 12" speaker is an OXFORD as 465 is the code for that company.
So I would assume that it was made in April of 1967.
Does that sound reasonable to you guys?

The 810 on the magnet must simply mean 8 ohm and 10 something?

12k5-7 or is it a 1 at the end? Maybe has to do with the magnet, quality level, etc.

Here's the link for the info:
http://home.provide.net/~cfh/pots.html
 

capnjuan

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Archer993 said:
... (1) I'm totally confused by the whole reverb circuit.... (2) The green wire is coming off of the regular speaker terminal, not the reverb speaker. (3) Did someone reverse the black and white wires on the regular speaker. (4) Could the filter caps, having malfunctioned, fried other components down stream.

(1) It's an acquired taste ... there are three ways to couple a reverb can to a circuit; transformer (Fender, Gibson, most of the known universe), capacitor (principally Ampeg), and a speaker (Guild). The supply signal for the reverb can is taken from the 12" speaker (not a 10"), through the R and C, into/out of the reverb can, back up to the stand-alone reverb amp, and into the 12AX7.

The reverb amp has its own dedicated 6BM8 power tube ... and odd-ball triode/pentode ... two tubes in a bottle. When the reverb is foot-switched off, the dry signal is amplified by the 6BM8. When the reverb is foot-switched on, the 6BM8 sees the signal from the 12AX7. The 6BM8 has its own output transformer (that you might be mistaking for a reverb transformer) next to the reverb amp. The 6BM8 drives its OT and the 8" speaker produces the wet signal.

(2) Fine; provided it's connected to the + terminal, it's supposed to be connected there.

(3) Two ways to find out if the leads are reversed; fire up, listen, change them, and listen again. One configuration will sound noticeably better than the other. Alternatively, go to the Bulgin jack on the chassis; the negative or ground side will be obvious; that lead should be terminated on the other-than-green-dot speaker terminal.

(4) Maybe but so long as there's a signal ... no matter how trashy ... coming out of the 8" speaker, then there's signal going in the 12AX7 and then to the 6BM8, and on to the output transformer, and the 8" speaker. Unless the can or dropping resistors show scorching or other signs of excessive heat or catastrophic failure, chances are nothing major is ruined.

Oxford speaker: I'd be inclined to read that as the 4th week of 1967. The speaker is 8 ohms; those other codes ... who knows ... sometimes they're for the type of cone and other details but prove the impedance thing to yourself. Set your meter to ohms and read the resistance across the two speaker terminals ... ought to read between 6.5 and 7.5 ohms - same for the 8".

12k5-7: I don't know what it means ... it could be a batch #, QA/QC #, order # or it could be one of these ... :wink:
 

capnjuan

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Archer993 said:
... Did someone reverse the black and white wires on the regular speaker.
Very well could be. Another T1 RVT just showed up on eBay. The auction amp speaker on the left below with the white wire terminated on the green-dot speaker lug. Your speaker on the right w/ pic rotated 180 degs showing black wire terminated on the green-dot lug. Also, auction speaker is an Oxford like yours ... v1 T1s sold with 12" CTS although they stuck with CTS for the 8".

comparespeakers.jpg



From the auction pics; closeup of the reverb-in connection at the reverb amp. Provided it's actually physically connected, your reverb terminates in the same spot. Your amp has a bare wire flopping around ... not shown in the auction amp. See also heater wiring on top of circuit board suggesting that all the v2s were done that way. Oh well ... never say never with Guild.

reverbconn.jpg
 

Archer993

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YES, thanks for pointing that amp out. Just when I was feeling bad about buying this amp which cost me $325 when the dust settled. Mine is in far better cosmetic condition.

The reversed wires on the main speaker could make a difference, but that's easy to check as the plug into the chassis is not polarized, just keyed.
The finger jointed pine comment in the ad may verify my is that way as well—without pulling tolex.
Speaking of the tolex mine has sloppy tolex as that one does too.

I pulled the reverb can cap last night in anticipation of a parts arrival tomorrow. The 60/40/40 measures 46/27/33 so it's a bit weak BUT is it too weak to mess op the reverb?
 

capnjuan

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Archer993 said:
... I pulled the reverb can cap last night in anticipation of a parts arrival tomorrow. The 60/40/40 measures 46/27/33 so it's a bit weak BUT is it too weak to mess op the reverb?
It's not so much about capacitance but whether it leaks; if it doesn't leak then I don't think the filter caps are the source of the problem.

I do think that floppy bare wire needs attention. If it's just a drain, then one end usually isn't terminated. If the can end is fitted with an rca plug and the bare wire is connected to ground at the can, then you need to carry the ground to the chassis somewhere. You might even try tying it off on the stand-off ... it's right there ... if it helps a little, then you might want to make a serious attempt to ground it correctly.
 

Archer993

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capnjuan said:
Archer993 said:
... I pulled the reverb can cap last night in anticipation of a parts arrival tomorrow. The 60/40/40 measures 46/27/33 so it's a bit weak BUT is it too weak to mess op the reverb?
It's not so much about capacitance but whether it leaks; if it doesn't leak then I don't think the filter caps are the source of the problem.

How can you determine if there is a leak?
 

capnjuan

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Archer993 said:
What floppy bare wire?
See the pic; the auction amp doesn't have that wire there; it's either grounded on the nearby terminal strip or it's not necessary and just not there.

loosewire.jpg


My understanding is that testing for leakage means taking them out and testing them on the bench with a power supply. Otherwise, I don't know how to test them while still in the amp. But consider that if your goal is the best-sounding amp you can have and the ps caps are original, that makes them over 40 years old.

Good practice would be to replace them so you have the highest chance of the best performance. If you do so, you will have (1) ensured the best performance, (2) cured the problem if that's what it was, or (3) be secure in the knowledge that you know what it isn't since you've done away with a common source of problems. If all you do is confirm whether the caps leak or not and find that they don't; what are you going to do; leave them in there?

Crappy sound can be a function of several problems at the same time. I'm familiar with the concept of 'getting lucky' ... finding the one (and only) thing that's making the mess. I hope you only have one problem to find ... that is, I hope you get lucky :wink:
 

Archer993

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I've never been lucky. everything is done the hard way.

The silver wire is the ground for the cable and does attach under the reverb board.

As you said in an earlier email, this amp has been messed with so it makes it all that more of a puzzle.
 

capnjuan

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Ok; so long as the bare wire is terminated somewhere.

Think of it this way; you have Darryl and I ... a couple of <ahem> older Americans ... over on the sidelines ... in our pleated skirts, white tennies, ankle-high socks, varsity sweaters, and pom-poms cheering you on. Okay ... you might get sick looking at us ... but we're cheering like crazy.

You can expect your luck to change ... one way or the other :wink:
 

Archer993

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Think of it this way; you have Darryl and I ... a couple of <ahem> older Americans ... over on the sidelines ... in our pleated skirts, white tennies, ankle-high socks, varsity sweaters, and pom-poms cheering you on. Okay ... you might get sick looking at us ... but we're cheering like crazy.

That image alone, of older Americans on the sidelines, in female attire, will sustain me throughout this project.
Thank You... :lol:
 

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Archer993 said:
Think of it this way; you have Darryl and I ... a couple of <ahem> older Americans ... over on the sidelines ... in our pleated skirts, white tennies, ankle-high socks, varsity sweaters, and pom-poms cheering you on. Okay ... you might get sick looking at us ... but we're cheering like crazy.

That image alone, of older Americans on the sidelines, in female attire, will sustain me throughout this project.
Thank You... :lol:

Holding cigars and Stoli, instead of pompoms, I think. :wink:
 

Archer993

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No parts order today due to some kind of UPS mess up :cry:

So I am of course looking for trouble in the amp and I may have found it. May.

The resistor at the bottom right of the photo has been replaced at some point. See the gold band instead of silver like the others (although there are several gold band resistors under the chassis that look original), however, it was a very sloppy solder job as evidenced by some extreme heat on the opposite side of the board and bubbly solder. The resistor in question is 470 ohms. If I look at the schematic it looks like 47 ohms OR maybe 4.7 mega ohms, BUT I can't be sure due to file legibility.

Does anyone know what this value should be? Thanks.

ReverbBoard.jpg
 

capnjuan

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Archer993 said:
Does anyone know what this value should be? Thanks.
470 ohms 1/2 watt. It's the screen dropping resistor. It's the only 47-anything resistor on the reverb amp. Confirm that it's connected at one end to the 220K resistor and to pin 7 of the 6BM8 at the other. The gold band indicates 1% ... it's a precision resistor to keep the screen voltage from fluctuating. You might consider a 1 watt replacement.

6bm8screemresistor.jpg
 

Archer993

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You are correcet sir. I was hoping it was the other 47 something resistor shown on the diagram near the reverb switch and reverb pot.

In any case something created a lot of heat at that resistor. It still tests OK though. Will up the wattade for sure.

Thank you again for the guidance.

capnjuan said:
Archer993 said:
Does anyone know what this value should be? Thanks.
470 ohms 1/2 watt. It's the screen dropping resistor. It's the only 47-anything resistor on the reverb amp. Confirm that it's connected at one end to the 220K resistor and to pin 7 of the 6BM8 at the other. The gold band indicates 1% ... it's a precision resistor to keep the screen voltage from fluctuating. You might consider a 1 watt replacement.

6bm8screemresistor.jpg
 
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