Guild 200S on the eBay

jp

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I gotta plug our resident Guild amp expert matsickma on this one. Boy, if I had the dough I'd grab this one off of you, Mike. My curiosity is extremely piqued. Stereo and EL84 power section, jeez what a beast! Good luck on the auction.

Guild 200S Stereo Amp
 

capnjuan

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About as cool as they come. Guild's version of a stereo amp like Gibson's GA79, GA83, and GA90; common power supply but two audio channels. Interesting little detail; instead of mounting the diodes on either a separate board or on the end of the circuit board; they put in an octal tube socket, wired the diodes to the socket, and brought the secondary AC to the socket; would keep them a little cooler with some air circulating around them. Good luck with the auction!

200Srectifier.jpg
 

matsickma

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Hi Guys,

This is a pretty cool amp that I rarely use. Somewhere along the way in the past few years that I owned it the 2nd channel started to act up. I figured somone with the right stuff in amp repair could pick this up at a reasonable price.

To clairfy the two points mentioned above:

1) power tubes are EL34 not EL84.
2) the solid state rectifier is not stock. A previous owner made this change.

Should I make those points more clear in the auction?

M
 

capnjuan

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Sorry Mike; after re-reading the auction, I see the information on the rectifier ... I guess it was there all along ... I always look at the pictures first :oops: Anyway, you're telling prospective buyers it's not stock .. as good as it gets. If it's handling 4 EL34s, then the rectifier must have been an 5AR4/GZ34? Without a standby switch, those diodes will put DC on the plates before the cathode filaments have had a chance to warm up ... stripping electrons out of the cathode coating faster than would happen if the filaments were completely warmed up. Not the end of the world but over time it will shorten the useful life of the tubes.

If the 5V rectifier filament supply is still there - pair of yellows, you could put it back stock. If the two high voltage secondaries aren't already there, put them on pins 4 and 6, the two yellow heater wires on pins 2 and 8, and connect the DC output the filter cap at pin 2 or 8 ... stick a GZ34 in there and you'd be good to go. I guess it would mean taking down the auction but it's really okay as it is. If you get buyer flack, you could always put it back stock in 30 minutes. John
 

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Hi capn,

Good info. I'll check out the wiring one of these days when I get home at a reasonable time from work.

The amp does have a StandBy switch. It is an odd little thing, similar to what Guild did on the early MasterAmps. They use a little slide switch for the StandBy function. It is located above the Ext Speaker jack.

When I look at the wiring of the StandBy switches of some Guild amps it looks like all it is wired to do is disconnect the "preamp" signal from the Power stage. Is that normal? I had always thought that Standby switches also changed bias to the power tubes. Your explaination above suggested that indeed more than just removing the input to the Power stage occurs with the StandBy switch is used.

M
 

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Actually, the standby switch should disconnect the highvoltage from the circuit, saving wear and tear on the tubes. Of course tube life wasn't an issue when you could walk into a hardware store and pick up RCA 6ca7's for fifty cents. :cry:
 

jp

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matsickma said:
Hi Guys,

This is a pretty cool amp that I rarely use. Somewhere along the way in the past few years that I owned it the 2nd channel started to act up. I figured somone with the right stuff in amp repair could pick this up at a reasonable price.

To clairfy the two points mentioned above:

1) power tubes are EL34 not EL84.
2) the solid state rectifier is not stock. A previous owner made this change.

Should I make those points more clear in the auction?

M
No, it's crystal clear. It's just my weary eyes from the days work leading me astray. EL34 it is and not quite the same beast I thought it was. :oops: Yet still very cool. I did note the SS rectifier swap out. I think it's still a great deal on an interesting amp for someone who's a little solder savvy.
 

capnjuan

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matsickma said:
When I look at the wiring of the StandBy switches of some Guild amps it looks like all it is wired to do is disconnect the "preamp" signal from the Power stage. Is that normal?
PhillyAmpzSteve said:
Actually, the standby switch should disconnect the highvoltage from the circuit, saving wear and tear on the tubes.
Hi Mike; I was looking for a toggle switch which normally has a higher power rating on its contacts than slide switches because, like PhillySteve, I was thinking it was interrupting the high voltage. On the 66J and 98RT, the standby switch opens the center tap on the secondary killing the power but you're right about the later models; Guild usually opened the audio circuit with the standby switch.

This isn't an issue with amps that have tube rectifiers - like the 200S originally - because their filaments take so long to warm up before conducting providing a chance for the tube heaters to warm up preventing 'DC shock' at turn on. On amps with ss rectifiers, the diodes produce DC the instant the amp is turned on so the standby switch usually interrupts the high voltage allowing the tubes' heaters to warm up before they see any DC.

It's a great amp in near-pristine condition; I hope it brings its real value at auction. J
 
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Hi Guys,

First time on the forum here. I found this site when searching for info on the 200-s amp. I recently bought one from my local music store and was surprised to see that it was this exact amp, SS rectifier mod, problematic second channel, etc. :D

Matsickma, can you tell me a little about its history? The ebay auction has expired and I can't view the page anymore. There doesn't seem to be much info about these amps on the net in general.

And for my most important question, does anyone have a schematic for the amp?

Thanks,
Chris
 

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Hi Chris!
Unfortunately, I've never seen a schematic for one of these. Given enough time, I could probably draw one, but that would entail a lot of sleeping on the couch at your house. :roll:

If you are able to pull the chassis and take some gut shots, our wily cap'n can most likely give you some help. :mrgreen:
Steve
 

capnjuan

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Emperor-TK said:
... And for my most important question, does anyone have a schematic for the amp?
Hi Chris and welcome to LTG. Over the last several years, we've pooled all the schematics that we've been able to find and so far, no schematic for a 200S ... but you're welcome to look around in the usual places like Schematic Heaven under Bargain Bin, Prowess Amps under miscellaneous, Audio Electronics Schematics, MusicParts.com under Guild or any of the other on-line sources ... I hope you find one. We might be able to tell you a little more about it if you can pull and ID the tubes and post some close up shots of the component side of the chassis. Congratulations on your very rare Guild amp and welcome to LTG.

(I was only wily once or twice last year :wink: )

CJ
 
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Well, since there doesn't seem to be a factory schematic available, I traced the amp myself. The rectifier and power transformer are definitely not stock. I'm not 100% sure that the amp shipped with EL34's either, since the Jensen C12P speakers weren't the highest wattage speakers available from Jensen at that time, and are rather underpowered for a pair of EL34s in class AB. However, the cathode bias resistors are period correct, and the tube sockets look original, so it might have non-original speakers, or just might have been a bad choice in speakers. It's possible that it originally came with 6v6 tubes though. "EL34" was written in marker next to the power tube sockets, suggesting that this wasn't standard. What do other guild amps from this era tend to use?

Regarding the bad channel: It was a blown speaker. I'm having Weber recone them to a 50W rating.\

Regarding the SS rectifier: The original power transformer was replaced with one from a Twin Reverb, so no 5V rectifier heater tap. Hence the switch to diodes.

My schematic is posted here:
Guild 200-S

One gain stage! But that doesn't stop the amp from sounding like Townshends amp from Live at Leeds when dimed!
 

capnjuan

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Hi Chris; you're gonna have to wait for matsickma on this amp; he knows more about this model than anybody here ... nice job on the schematic. CJ
 
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I just had another look inside. I'm changing out to a grounded power cable tonight. I'm 95% sure now the cathode resistors aren't original. The solder looks too shiny compared to the other connections and they don't quite fit between the eyelets. I'm now thinking the EL34's weren't stock.
 

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I had two 200-S amps over the years and both were EL34's. I seen a few more in auctions and they were also EL34 amps. I think the 200-S is the only guitar amp that Guild used EL34's. In the late 1960's Guild made a PA power amp for rack mounting with a pair of EL34's.

M
 

capnjuan

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Emperor-TK said:
... I'm 95% sure now the cathode resistors aren't original. The solder looks too shiny compared to the other connections and they don't quite fit between the eyelets ...
Hi E-TK; the fact that the cathode resistors might not be original doesn't necessarily mean it was converted to an EL34 amp; if it's got a Fender PT in it then somebody spent some quality time with it and that could have included updating the cathode resistors and bypass caps if the amp uses them. Got some pics of you amp? CJ
 
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Hello all, first post here. I really enjoy this site and this post caught my eye. I'd like to learn more about the Guild Model 200s / Twin amps

I just missed out on buying one of these 200s amps last week...I showed up at the store just as they were closing and it was gone before I got back a week later. Unfortunately, I never got to play through it before it was sold. It's unlikely that I will find one anytime soon but can anyone describe the tone of this amp? Does it do cleans well? It seems that it would make an awesome stereo amp but I am not certain how good the EL34 clean tone would sound.
 
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