New to forum with my superstar amp and have questions

[steveo_4]

Howdy, y'all.
I've been reading a lot of these posts since I acquired a superstar amp (serial # S1076) about a month ago. Wow, plenty of great info. Already got the schematic through here, so a big thanks for that. If anyone has a digital copy of an original owner's manual I'd greatly appreciate it. Can the amp be dated from serial #?

My name's Steve and I live in NH, currently awash with political goofiness. I love the look of this amp. two-tone grill does it for me. I wanted a more powerful complement to my Silvertone/Danelectro built 1432. I'm pretty sure this super-silver line-up will rock! It'll be a great clean-dirty set-up.

The amp didn't have a back, so the pictures I found here helped immensely in my construction of an accurate birch ply replacement. Thanks again!!

I've taken it all apart to clean and search for obvious problems, and there were none. All components appear to be original, or at least really old. It cleaned up real nice, and I know I need to get it serviced(caps, three prong{didn't I read about a death cap?}), but I couldn't wait! Fired her up slowly with a variac, no problems. Replaced preamp tubes with some JAN-CKR 12ax7's. It works great, reverb kicks, don't know about trem yet, have to build a switch...BUT...
here's where my questions begin......

I know there should be a 7247/12DW7 in the hole next to the power tubes, but there is a 12ax7 there. I understand the difference, and the potential for damage, but is there any audible difference?
Also, there were a pair of 6l6wgb's in the power slot. When cleaning/ inspecting, I was looking to see if any modifications had been done to accommodate those tubes, but it did not appear so. I'll be dropping in some vintage 6L6gc's instead. How do you use the bias control on the superstar? I'm guessing one voltmeter probe in center, one outside- but how specifically? and meter settings? bias settings?
And what's with the hum control? how do you use that? will that hum control do anything once there's a 3-prong cord on there?
Boy-oh-boy, I got questions....

I'd really appreciate any help, even a link to a buried post. I've looked through a lot of them, but I'm sure I've missed a few.
Thanks in advance for any help. and once more, a copy of the original owner's manual would be super!

Live Free or Die,
Steve

 

[fronobulax]

Welcome, but alas, I have no answers for you.

 

[steveo_4]

That's okay, it's nice to be welcomed! I'm sure someone out there possesses the knowledge I seek....

 

[Default]

Waves.

I'll chip in some pertinent stuff at lunch, don't have time now. Yes, there should be a 12dw7 in there. Tonally, there might not be much of a difference, but the voltage is higher than a 12ax7 is looking for. I would get a NOS 12dw7 or a JJ new manufacture. You want to save the ax7 for the tone circuit.
Hum balance is a tune by ear system. Find the spot where there is the least amount of hum and leave it at that.

 

[Default]

Btw, pics would help greatly!

:-D

 

[steveo_4]

I'll get some pics together this afternoon.
Thanks for the info on the 12dw7 and hum balance.

Boy, you guys are quick to respond! Thanks!!

 

[steveo_4]

I'm tryin' to set up a link to a few photos- here goes-

https://picasaweb.google.com/lh/photo/F ... directlink
https://picasaweb.google.com/lh/photo/U ... directlink
https://picasaweb.google.com/lh/photo/y ... directlink
https://picasaweb.google.com/lh/photo/b ... directlink
https://picasaweb.google.com/lh/photo/J ... directlink

let's see if that works.
A couple knobs have been changed, and there's some pinstripe added along the way, but all pots/switches are in good shape. The red power light does not come on, and I need to source a replacement handle.
I don't know what the speaker is, but it ain't the Jensen they offered.
The bias control has two holes, I'm guessing for voltmeter probes?, and two screw adjustments opposite each power tube.
the new back, not yet fastened to the cabinet: I don't care if it's covered with tolex or not, but to cover the bare birch ply I used a textured spray paint. It looks a lot better than just paint, and it has some, well, texture to it. I figure havin' a back on will get me closer to what this 75lb. beast sounded like when they built it.
Any thoughts?

well, the links work...

 

[Default]

I wouldn't automatically assume that it came with Jensens. Usually, the stock speakers were CTS and the upgrades were JBLs, but like I said, I only have phone internet and it's too painful to search on it.

Edit/ there should be a six digit code on the speaker. Post it please?

 

[steveo_4]

speaker codes: 69-6705 0108022 it's a big square magnet(ceramic?), 15" cone. no other markings.

 

[matsickma]

The stock speaker on my Superbird was a black speaker.(I see if I still have it around.) I was not a full range speaker and was pretty dull on thge upper end. Guild didn't specify the name of the base model speaker so it may have varied overtime. The two speaker upgrades were 1) EV SRO and 2) JBL D130.

BTW it looks like youyr amp has EL34's instead of 6L6's. The stock configuration was 6L6.

M

 

[steveo_4]

the tubes you see in the photo are Chinese 6L6wgb 'blues tubes'. I plan on replacing w/6L6gc's. I have a few sets of matched vintage tubes lying around, that's why I'm asking about the bias controls. If anyone had a digital copy of the manual, I would think how to use those adjustments would be in there. but, I don't know.

 

[SFIV1967]

Welcome to LTG Steve! I am linking your pictures to make it easier to see:

Ralf

 

[steveo_4]

Thanks for linking the photos- I appreciate it!

 

[SFIV1967]

You're welcome! You just need to include the link to the "*.jpg" files (I right clicked and copied them from the properties of your pictures) and put them between the "

" signs (where you see the "%20" currently in my post here). It's the button above in the menu when you compose a message.
Ralf

 

[Default]

Re: the bias trims

Right next to the test connections, there should be a number followed by mv.

Set your meter on the millivolt range and adjust the trimpot for each tube to that number. Guild rocked when it came to their amps an the technical features. There were other amps that fed dc voltage to the heaters, but Guild was the first company to make it standard with a purposely designed circuit.

Shame they weren't more popular.

 

[steveo_4]

cool! There is no number next to the bias adjustments, but on the schematic, next to 'bias control', is .414. I guess that would be mv. There are only two probe holes- so I'm confused- is it one probe hole for each power tube(2), and ground probe to chassis? or something else? I don't really understand that section of the schematic. If you place both probes in the test holes, how do you know which tube you're adjusting? Is this a forest thru the trees thing? What am I missing? I need a little more help, please. and the help is greatly appreciated......

 

[Default]

One probe to chassis, one to a testjack "hole". Yep.

 

[steveo_4]

Thanks, man. Can't wait to try it out tonight.
Any other adjustments necessary? I know on certain Fenders you adjust bias & balance.
gonna build a switch tonight to check trem circuit. I'm guessing 'cause it's an RCA input for the switch, a simple switch connecting tip & ring will suffice?
I really appreciate the help y'all are offering.

 

[Default]

That's what I get for posting on the run. That .414 is .414 volts. The other part to your question - each tube has it's OWN bias control - no need for a balance control. That means, you can use whatever tubes you find without them having to be matched. Find an unused pair of RCA blackplates at a garage sale? Plug them in, bias them up and you are good to go.

 

[steveo_4]

Actually, that's what I'd like to use: An RCA blackplate and a Dumont w/code 73-13 I have . So, if the voltage is .414, that's what I'm adjusting each tube to read, right? thousandths of a volt.....

I'm just tryin it out- right now, with the pair of Chinese 6L6wgb "Blues tubes", the readings are .332 and .289. I don't think I want to crank those up to .414 'cause they(wgb) can't handle the higher voltage, or so I read.
I won't have a chance to put in the vintage tubes for a day or two, but I'm curious about how hot I can bias them. But, To do that, am I correct in saying I'd need the tube data to not exceed capability? Is there some kind of 'rule of thumb" for cold vs. hot biasing given a voltage of .414? Vintage vs. new tubes? Hee vs. Haw? American vs. national league?
or am I really overthinkin' this........

you're assistance is great.