Thunderstar Bass Amp

ThunderCat

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stuck

I tried to take out the chasis of my Thunderstar and it gets stuck on a wooden ridge on the inside of the cabinet. One way the transformer is too big and the other way the front panel is too big. Also it seems liek some else has worked on it as there are chips out of the sides where it can get stuck. I feel like chiseling off the top ridge....would this be bad?
Anyone worked on one of these?
 

matsickma

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Hold on Thundercat!

The amp housing comes out from the front not the back. Look closely at the sides. You will see and pan head bolt on each side near the front about a third of the way down. Remove these and you will be able to remove the front black plate with the Guild emblem on it. With thit done you just slide the amp out from the front.

matsickma
 

megadan

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ThunderCat said:
Here are some pics of my Guild Thunderstar Bass amp. It has a bad hum but it seems to work ok. I dont know what its suppose to sound like but its fairly clean and warm. Do these amps overdrive?

It's warm and clean, but it should overdrive nicely. I have a Quantum, which overdrives nicely at high volume playing bass.

If you play guitar you might want to hit it with a clean boost or something like a tubescreamer.


My Quantum had a bad hum which I assumed was bad caps, but then one day after a year of owning it, I adjusted the hum balance, and lo and beyold! The hum was gone. Try it if your amp has a hum balance.
 

ThunderCat

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ya

Hi, I tried the hum balance and it didnt do much. I bought a new three prong chord and plan to try and ground it. The power supply for this amp looks tricky. The path goes to a ac outlet, then the white wire goes to the back of the fuse, then both go to the power switch. You can see it in the pictures.

Matsickma have you converted a Guild amp to 3 prong?
I found this webpage which seems pretty good.

http://www.tonecraftamprepair.com/html/ ... conve.html
 

megadan

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I had mine converted to 3 prong; I can't really say how much it did for hum, as it did it as soon as I got it for safety reasons.
 

ThunderCat

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ya

Well it looks like I need a full cap job for this amp. The hum is just too much to take. One can (black) doesnt seem to be connected to anything? Does anyone have a schematic for this Thunderstar Bass amp?

thanks
 

capnjuan

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Hey ThunderCat:

How'd you make out with your amp? Did you get Howard's schem? Caps done?

Where are you on the 7591s/6L6s? 7591s running $30-$40/ea

http://search.store.yahoo.com/cgi-bin/n ... earch.html

http://search.store.yahoo.com/cgi-bin/n ... index.html

I use EH 6BM8s/12AX7s and JJ 6V6s/12AX7s; happy with both brands.

If you're still hum-hunting and if the tubes pass a signal, they are probably down the checklist a ways; caps, grounding, leaking interstage coupling caps (the smaller ones), crummy pots w/ cracked carbon or cermet resistive elements - the cap with nothing connected comes first for hum and safety reasons - see below.

The AC power cord isn't a noise issue; it's a safety issue. If something let's go, it can put several hundred volts of DC on your chassis not to mention your pickups.

Apologies if I overcooked the 7591-6L6 reply; the 7591 is coming back into decent supply; if you can hang on, the price may dip to the point where you'd have to run through alot of 6L6s to offset the expense of re-wiring to support them - unless of course you do it yourself.

Member here? http://www.webervst.com/bns/ Lots of people buying selling each other tubes; 7591s come and go from time to time.

Happy to help if I can.

cj
 

ThunderCat

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hi,

Oh Hi, Capn! I just took it to my electronics buddy today. I havent had time or the right parts to get it fixed. It probably just needs some new caps and resistors. Looking closely, I could see some burnt out resistors. I am hoping the mismatched 6l6's (ones a GB) are fine. I've never tried an amp with a tube rectifier. The schematic from Howard doesnt have one. Speaking of tubes! My friend gave me his old Hammond s-6 organ. Its all tube tone generated, so it has about 30 tubes all Hammond labeled RCA's. 18---- 12Au7's, 3--- 12ax7's, 2-- 6v6's, a 5u4 , and some others. I fixed the volume control and the organ works fine. It's tempting to use it for parts.

I'll keep you posted.

thanks
 

capnjuan

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Howdy TC:

If you have the schematic in electronic format, send it to me - look for my email address in PM. Warning: if you spam me, I'll make a voodoo 'tube' out of a 6L6 - short circuit it or something - your amp will never work correctly...kidding of course....sort of....

I have dozens of carbon comp and metal film resistors; 1/2 and 1 watt and 5 and 10 power resistors; free to a good home. Also have one remaining 3X40uf/450V Weber multi-section cap w/ mounting hardware...ought to do it for your unconnected can-cap; how many multi-sections are in there?

Nothing wrong w/ tube rectifiers; rugged, reliable, and in good supply although they are more prone to 'sag' which, depending on your point of view can be good or bad; alters tone some but one man's treasure is another man's trash. During the mid-60s, alot of manufacturers transitioned to solid state / diode rectifiers; chances are Howard's schem is a later version of the same amp.

Tube amps with diode rectifiers need a 'stand-by' switch or position on the power switch. When turned on, a solid state rectifier puts B+ instantly on the tube plates however the filaments (heaters) need time to warm up. If they don't get the time, electrons are 'stripped' off the cathode stressing it and shortening the tube's useful life. Because a tube rectifier also requires time before it will conduct, amps using tube rectifiers don't have this problem.

Years ago I was fortunate to own a Marantz 10B tuner; Saul Marantz's 'last (tube) word' on the subject of tuners; 21 tubes including rectifier. Before you part out the organ amp, you might want to consider making sure you either have a schematic or can confidentally identify the value of components. As ever, the devil is in the details...2X6V6s...good for about 15 watts; I don't know the EL84 at all which has a similar power rating but 6V6s are pretty versatile; sharp and tangy to smooth and, depending on the speaker, break up nicely.

Leave your mis-matched 6L6s in the amp until the power supply is stabilized and you have a fresh cathode resistor with parallel cap; then you can get a matched pair; going to run $35-$50 - which is why the power supply and cathode cap need to be in place before you re-tube; if not, you'll have a brand-new mismatched pair instead of a used mismatched pair....

good luck...let me know if I can help.
 

ThunderCat

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Oh wow, I finally have my Thunderstar Bass amp up and running. Looking at the dates its been over four months. It took two months to get it back at first. I plugged it in and it blew the panel breakers (short circuit). Then it had a terrible hum. I was ready to give up on it. I am now going to do all my own repairs, even if I screw things up.
 

capnjuan

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Welcome back TC: let us know if we can help you get it right or you blow it up. If it goes up in flames, try and remember to get some video... :wink:

Chances are one/all of the subsections of the multi-section power supply filter 'can cap' is a dead short; no internal resistance to ground for the B+. Alternatively, it could be global warming, flatulence, or male pattern baldness.

Good luck!

cj
 

ThunderCat

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Ya...the bright orange glow of the jewel light could have real fire behind it. The chrome and jewel lights make the amp look good in the dark. I found one piece that was loose, probably from me putting the chasis back into the caninet. The amp works great! I really tested it last night, wow! This amp rocks. I had it cranked and it got a nice overdrive sound. I also liked the bright switch for clean stuff. I had it plugged at first into a 1x12 cab, then for more sound I pluged in another 1x12 which gave it more volume.
 

capnjuan

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Are the hum levels tolerable? Lights: ya know, you could check some of those sites that cater to the pickup truck after-market ... get some of those outside cab dome lights....or maybe a spinning yellow one like the road crews .... 8)

Glad that it works; could ya turn it up a little so Graham can hear it?


cj
 
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