For Sale: 68 Guild Thunder 1 Twin Guitar Combo Amp - Mint

adam79

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I have a 1968 Guild Thunder 1 Twin Guitar Combo Amp. It is in mint condition. The only cosmetic blemish is that one of the original CTS Alnico speakers does not have the sticker on the back. Pre-tubes are Telefunkens, and the rest of the tubes are labeled Guild, made in West Germany. All have low hours. The amp looks brand new. I'm asking $340. I got it up on ebay, here's the link: http://cgi.ebay.com/68-Guild-Thunder-1- ... 3ca7fcd233.

Thanks,
-Adam
 

Bill Ashton

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Perhaps someone knows...I understand why the reverb model had two speakers, delaying the signal to the second for the rever effect, but why would a non-reverb model have the same configuration? Were they using up baffle boards? Would seem that the savings would be offset by having to stock or special purchase a run of different output transformers...???

Way back in the late sixties, I acquired a used Thunder 1 Reverb from a friend...amp was shot, butchered attempt at a repair by others, I just wanted it for use as a speaker cabinet.
 

capnjuan

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Hi Bill; somewhere else, matsickma pointed out that this 2X10" non-reverb amp was marketed as a practice or light-duty bass amp. As such, reverb would be of no value but the second speaker would add to the total amount of air being moved ... perceived loudness and presence. Guild and Sano I believe are the only manufacturers from back in the day to produce amps with a 'reverb-only' speaker; it's just one of several ways to produce the effect. I think this amp model was intended as another way to market the T1 design/chassis; not just a combo amp for guitar but appeal to bass players too with the extra speaker. Otherwise, there's no requirement that says if you want reverb, you have to have a 2nd speaker to support it. J
 

Bill Ashton

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Cap'n, my mistake entirely, I thought this to have a 12" and and 8" , ( :oops: ) though by further enlargement it does in fact have two similar sized speakers. Fair enough for use as a bass amp, though the inclusion of tremolo would seem rather odd for that application...cannot quite make out what the two position switch is next to the "speed" control.
 

capnjuan

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Hi Bill; I see your point about tremolo in a bass amp but, just guessing, I think they built the chassis for guitar and then looked for ways to sell them by varying the speaker config ... maybe bring in some sales as a bass amp. If so, the trem was there whether a bass player wanted it or not. Guild continued the 'dual use' approach ... the Thunderbass series of heads had bass and guitar channels. That switch is a Bright switch ... puts an R/C filter in/out of the circuit. J
 

capnjuan

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Hi Adam; it's a class A/B amp, not class A. Brief but boring distinction; in your amp, one of the output tubes handles the positive half of the AC signal and when the positive half dissipates, the tube shuts off and the other output tube amplifies the negative half of the AC waveform, then cuts off, and the other tube ... back and forth, on and off, push/pull or A/B. Highly simplified, a single-ended amp is the best example of a Class A amp ... where the single output tube never shuts off ... it handles positive then negative, then positive ... Anyway, this is the broad brush distinction.
 

adam79

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What is the RMS rating on the Thunder 1 Twin?

Thanks,
-Adam
 

capnjuan

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Hi Adam: RMS ... root mean square is the ratio of mean output power to mean input power. RMS, as it relates to an amp's output expressed as watts, is commonly two times the rating of the amp ... something of a power-handling buffer to take transient spikes into consideration. If you're asking what's the rated power of your amp in watts, that design and its twin 6GW8s are rated at 10-12 watts.
 

matsickma

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I never fully understood how a Class A/B amp works but I it was my understanding that a Class A is single ended and the "Quiescent Point" of the amp is in the middle of the single ended voltage rail. A class B amp does the Push/Pull where half the power tubes amplify the + waveform and the other half of tubes amplifies the - waveform.

I beleive that a A/B amp is supposed to work in a manner that at low power it is in Class A mode while at higher power it is class B. If what I stated is correct then how does the Amp transition between modes and when does that occur?

I only know enough to be dangerous here so take what I posted with a grain-of-salt.

M
 

capnjuan

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matsickma said:
I beleive that a A/B amp is supposed to work in a manner that at low power it is in Class A mode while at higher power it is class B. If what I stated is correct then how does the Amp transition between modes and when does that occur?
Can't answer the question about transition and timing. I think your understanding about Class B amps is correct although Class B amps are distinct from Class A/B amps with respect to how they cut off; Class B cutting off sharply which induces some distortion and Class A/B with some overlap to diminish distortion.
 

capnjuan

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adam79 said:
What's an example of a Class B amp?
Hi Adam: Fender, Gibson, and others made twin output/'cathode biased' Class B amps ... so did many other mfrs. Class A/B amps are 'fixed-bias'; instead of inducing a 'grid more negative than cathode' condition by inserting a cathode resistor between the cathodes and ground, Class A/B amps relying on injecting a small negative voltage on the grid so that it is always more negative with respect to the cathode which, without its cathode resistor, is still always more positive than the grid.

More on the subject here from RockNRollVintage.com
More on the subject here from Kelly Industries
More on the subject here from Wiki

Or ... you can google 'Class A and Class A/B amplifiers' ... you can read all about the strengths and weaknesses of each type.

This is the only T1 / 12 schematic I have; this amp uses a negative voltage from the power suppy (magenta box) that goes through the trem controls to manipulate bias to get the owaowaowaowa ... and then to the grids of the output tubes. That negative voltage means the grid will always be negative with respect to the cathodes which are shown tied together ... without an intervening resistor ... and grounded ... Class A/B:

t1bias.jpg
 

adam79

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when i asked for an example, i was looking for a brand and model of amp, but thanks for the schematic.
 

capnjuan

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adam79 said:
when i asked for an example, i was looking for a brand and model of amp, but thanks for the schematic.
In an earlier post that he thought Adam would read said:
Hi Adam: Fender, Gibson, and others made twin output/'cathode biased' Class B amps ... so did many other mfrs.
We got a guy in another thread bitching because nobody answered his question; I answer yours in detail and I get 'tude.
 

adam79

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capnjuan said:
We got a guy in another thread bitching because nobody answered his question; I answer yours in detail and I get 'tude.

No "'tude" intended. All of you have been a HUGE help to me on this site. I appreciate all of it. I skipped a few of the more technical posts regarding the classes of amps. I was just asking if someone would name a Class B amp. I guess it was a stupid question that got misinterpreted.

-ADam
 

capnjuan

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Hi Adam; my apologies, a mis-read on my part. The Fender tweed-era Deluxe 5E3 is a Class B Push/Pull amp. By contrast, the Fender blackface-era Deluxe AA763 is a Class A/B amp. The easiest way to distinguish one from the other physically and schematically is how the output tubes are biased. There's somewhat more to it but those physics are past me. Shown below are the 5E3 and AA763 Deluxe amps. More down below if you're interested.

deluxeD.jpg


Bias refers to the fact that, at idle and in operation and for the tube to conduct (current to flow), the grid where the musical signal appears has to be more negative than the cathode. There are two ways to achieve that condition; force a positive voltage on the cathode (cathode-bias), or inject a negative voltage on the grid (fixed-bias). The AC signal appearing on the grid 'irritates' the tube and causes an increase in the flow of current from the plate to the cathode.

On the left in the red box, there's a resistor whose effect is to force a positive voltage on the cathode. On the right in magenta, is the negative voltage - like your amp if if matches the schematic (and it might not) that causes the grid to be negative. Since the cathode is connected to ground, its voltage is 0 although some designs including Guild heads put a small value resistor there.

The short of it is that Class B amps distort at lower volumes (sooner) than Class A/B amps; depending on how they're used, this can be objectionable. As matsickma pointed out, Class A/B amps at low volume operate like a Class A amp; I do not understand exactly how that happens.
 

adam79

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I sold the Twin for $300 cash; local buyer. I know I could have gotten more for it if I had waited, but I tried selling it for $400-350 for a couple months, and there were no takers. Now that I've sold it, I miss the amp.. but when I owned it, I barely ever played the thing. It doesn't really make much sense.
Now, the only Guild I have is an '81 M-80. I'll never sell that guitar, it's my favorite next to my Mustang. I used to have a '77 M-80, but ended up selling it; I liked the 2nd version much better. The only thing that the 1st version has on it's successors is it's looks. I'd like to play the 3rd version, it's the only one I haven't played/owned. There was one on Ebay a couple months ago; it went for $650.

Thanks you guys for all the help,
-Adam
 

capnjuan

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adam79 said:
I sold the Twin ... Now that I've sold it, I miss the amp.. but when I owned it, I barely ever played the thing. It doesn't really make much sense.
Hi Adam; congratulations on selling it and I can relate to that sense of 'loss' ... or whatever it exactly is. I sold or traded away 4 amps in the last year ... each of them in good condition with fine tone ... sometimes it's about not being able to justify hanging on to them; feeling pinched for the money, not getting played, prefer amp #3 over #2 anyway ... that kind of thing. Yes; I'd like to have them all back but if I did ... they'd still just be sitting there :( :) . Best, J
 
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