New member with new toy ( Thunder 1)

[capnjuan]

... While I have a bit of practical experience, you are obviously much more knowledgeable than I am about theory.

"In the land of the blind, the one-eyed man is king"

Thanks ... but I've just made more mistakes.

... As my dad taught me, and I'm sure you agree, never work with electronics when you are tired.

... or knocking back Heinies or sneaking out for a doobie ... If you get a corrected schematic, think about posting it here. Nice get with your amp; good luck! CJ

 

[Blues and Jazz]

CJ, this is my kind of place because no one takes themselves too seriously. The beer does come in handy though if you've burned your fingers while soldering. Apply topically and orally. : )

I hoped to hook up the new extension cord today but the existing strain relief was not re-useable. Radio Shack doesn't sell these anymore so the new strain relief was part of the Antique Radio Supply I just placed. So when I get the parts in I will share the details in a new post.

I will share the updated schematic when I get it done.

Best regards,

B & J

 

[capnjuan]

Agree; beer is a good thing ... if you're using either a #16/3 or #18/3 cord, you may find that the strain relief fitting means you have to enlarge the hole in the chassis. If yes, do it a little bit at a time ... trial and error ... until you get a snug fit. On occasion, I've had to resort to a 5/8" carbide-tipped drill bit, rags to catch the flying metal scraps, and a few Heinies (bottles only at juanzampz). Yes, it's a pretty good group here; good luck with your amp. CJ

 

[JazzWest]

Curious to know when Guild switched over the Thunder 1 from cathode bias to fixed bias? From what I've seen, most of the black tolex Thunder I and RVT's are cathode bias, but haven't examined a later, tan/fawn tolex ones (post '66)?

 

[capnjuan]

Hi Tommy; I think the only person who can maybe answer your question is matsickma; he knows more about these amps than anyone here. I thought they were all fixed-bias; this one was a surprise. It doesn't look converted ... it looks like it never had bias taps :?

 

[capnjuan]

Thank you capnjuan...

Thanked me too soon ... the box text above reading 'HV DC to Rectifier' should read: 'HV DC to multi-section filter cap' ... (burp) ... too many Heinies :lol:

 

[coastie99]

CJ, this is my kind of place because no one takes themselves too seriously.

B & J

Regretfully, not entirely true B & J. There are a few 24 carat anal-retents here ! But they lose.

 

[Brendan]

If anybody is interested, I have a number of NOS ECL86's that I'd part with.

I'd like to check back with you after Christmas....if you still have a pair available then. I have a list of parts I want to pick up for this project now, but I'm still expending all available funds on holiday goodies.

 

[coastie99]

If anybody is interested, I have a number of NOS ECL86's that I'd part with.

I'd like to check back with you after Christmas....if you still have a pair available then. I have a list of parts I want to pick up for this project now, but I'm still expending all available funds on holiday goodies.

Hi Brendan.

Sure, do that, but it's a case of first in, first served.

Cheers,

Gary.

 

[Brendan]

Thank you capnjuan...

Thanked me too soon ... the box text above reading 'HV DC to Rectifier' should read: 'HV DC to multi-section filter cap' ... (burp) ... too many Heinies :lol:

I started searching immediately for info on cathode bias and didn't catch that. :lol: I plan on replacing both the bias cap and resistor, but couldn't find a resistor with those specs anywhere. Lo and behold, a pair of those resistors showed up on ebay at a price I can afford now. 8)
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0293709904

Anyone have an opinion on Illinois capacitors? I'm not seeing any Sprague Atoms close to the specs of the first filter cap (50uf 450v)

 

[Default]

I've used Illinois caps in a fair amount of stuff. Physically, they're smaller than Spragues.

 

[Brendan]

Well I haven't let this slip to the back burner yet and I've been busy mapping out the chassis layout with a freebie graphics program. I'm looking forward to getting busy in January. Question - there's quite a few electrolytic caps past the filter stage. Can any of these be replaced with Orange Drops with the same specs?

 

[Default]

If you are talking about the 25 MF bypass caps on the preamp cathode resistors, I would just replace them with new.
If you are talking about the other capacitors in the below pic, yes, you can replace them with orange drops, if they are leaky.

 

[Guest]

capnjuan,
I recently acquired a Guild Thunder 1 without reverb. It is fixed bias. Will you please send me a copy of the schematic? Thanks.
Doug

 

[Brendan]

Hope everyone had a great Christmas. I'm about to order some of the parts and take advantage of Antique Electronic's 10% December discount. 8) I made an interesting discovery last night. On tube V4, there's a white wire and a bare wire in a black sheath that connect pin 1 (grid) to a nearby strip terminal. There's an odd .01uf capacitor upstream. Pic:

As I followed this wire assembly to pin 1, I noticed some discoloration at the socket.

Further inspection shows that bare wire (ground?) is not connected at pin 1:

I'm guessing that too much juice made its way to the grid. The resistors in this circuit are within spec. I was going to replace the two caps upstream, but is there anything else I'm overlooking?

 

[capnjuan]

Hi Brendan; using your meter or a continuity tester, check the resistance to chassis ground from the junction of the bare wire and the terminal strip it's tied to. If that is ground, then what you have is a shielded jumper from the wiring strip to V4A/pin 1; the other end at the pin isn't supposed to be terminated; the idea is to protect the signal from stray EMI and drain it to ground; shielding is normally terminated at one end only. As for the sooty stuff at pin 1, looking at pics, I can't tell if it's a function of electrical trouble or not ... maybe just some inartful soldering? Try a toothbrush and some alcohol ... see if you can clean it off. CJ

 

[Brendan]

Thanks capn! I have continuity to chassis ground. Phew!

One last question - there's 3 32uf 4v capacitors coming off the cathodes ( 2 on V1, 1 on V3). I've searched high and low and cannot find direct replacements. Nothing but big filter caps at 32uf. I have found some low voltage 25uf and 50uf. Not quite as small, but I can work around that. What kind of change could I expect with either of those?

Thanks for the help!

 

[capnjuan]

Hi Brendan; those are cathode resistor bypass caps. Replace them with 25uf/25v Spragues if you can find them, any other brand is ok. Their precise value isn't that important but their voltage handling is. Their value contributes to the tube half's bias setting and it's frequency response. More here: Voicing Amps There will not be a quiz :wink:

 

[Brendan]

Thanks, capn. I ordered up the right bits. Thanks for pointing me to the good reading materials.

Ah yes, USPS brought me a gift today. Lots of new shiny caps and a few resistors. As I disconnected the old cord from the power switch, I noticed that the top two lugs of the power switch seemed a bit wobbly. I'm not sure how prone a power switch is to failure, and I suppose this one will work, but I'm noticing that other overhauls posted here at LTG replace the switch. Damn, there goes my shiny red button, huh? So has anyone found one that is a direct swap? I'd rather not mess up the face panel.

edit: This one looks like it would work ( at bottom of page)
http://www.mcmaster.com/ctlg/DisplCtlgP ... 5161595964

All the mounting and cutout dimensions are exact. I suppose this must be a standard size? I'm not crazy about a nylon housing.

 

[capnjuan]

... I noticed that the top two lugs of the power switch seemed a bit wobbly. I'm not sure how prone a power switch is to failure, and I suppose this one will work ... Hi Brendan; every time that switch is operated and as the contacts close, there's a little arcing. Over the years, the contacts inside the switch eventually burn and corrode and the switch fails either 'open' - switch doesn't work at all, or 'closed' stays on or off depending. The wobbly thing isn't uncommon on slide switches. Given the age of the switch, the modest cost / hassle to replace it, the fact that you can hang onto the red one if someone wants to put back to authentic, and how pissed you'd feel if spent hours on it only to have the switch fail in a few months ... yes; good bye red ... edit: This one looks like it would work ( at bottom of page) Yes, so long as it's not a minature or sub-minature, it will work. CJ