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Old 20th February 2012, 04:25 PM   #1
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Default 1970s fender champ givin me problems

i know next to dick about tube amps. my roommate has a fender champ i think its a 1970s model with only three knobs on it. we thought it had one blown tube because when we turned it on only one of them lit up. today i bought a set of Groove Tube 6v6 or something (based solely on the advice of one of the guitar center guys. i replaced the tubes and still the left tube wont light up. is it the socket? do i have to bias it or whatever? gimme feedback im basically a retard when it comes to this stuff. kthnx
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Old 20th February 2012, 06:19 PM   #2
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Sounds like the heaters/filaments are not powering up. The old tubes may be just fine....

The tubes need the heaters (filaments) to warm up and operate properly. That's why in the old days you needed to wait a few seconds for the amp to warm up.

Since one tube heater is working, it's likely that the transformer filament winding is good, you just have to determine why the others are not lit up.

Do you have a multimeter? Are you comfortable working around high voltages? The heaters run at 6V or 12V, but other parts of the circuit operate at several hundred volts.

You may as well remove the amp from the enclosure, and if possible snap and post a couple of pics, that will help troubleshooting.

Is there a label on the inside of the amp enclosure? It should have a circuit designator, a few letters and numbers (like 5F1 or AA768, etc). That will tell you what schematic it uses, as well as the tube compliment. You should be able to find the schematic online easily with the circuit identifier. These circuits are very simple, and this should be easy to troubleshoot.

Last edited by boywonder; 20th February 2012 at 06:25 PM.
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Old 20th February 2012, 06:53 PM   #3
Gilgy is offline Gilgy  United Kingdom
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I'm a bit worried when you say "a set of 6V6" because that amp only uses a single 6V6. The other tubes are a dual triode and (in older models) a 5Y3 rectifier. Do you know exactly what tubes you've put into the amp?
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Old 21st February 2012, 02:34 AM   #4
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Quote:
Originally Posted by Gilgy View Post
I'm a bit worried when you say "a set of 6V6" because that amp only uses a single 6V6. The other tubes are a dual triode and (in older models) a 5Y3 rectifier. Do you know exactly what tubes you've put into the amp?
I must admit, I know little about the Blackface/Silverface models, but to my knowledge the basics of the 5E1/5F1 circuits continued through. That is, a 5Y3 rectifier, a 12AX7 dual triode for the pre and a 6V6 as the power tube.
The 5Y3 and the 6V6 are both Octal (large plastic base with 8 pins and "keyed post in the middle to stop you putting the tube in the wrong way) sockets and the 12AX7 is a Noval socket (9 pins coming straight out of the glass tube, much smaller than the Octals)

Straight out, I'd be inclined to advise that you take the amp to a Tech to have a look at. I get the feeling you don't have a large amount of knowledge when it comes to electronics, and there are several hundred volts lurking inside that amp, even when unplugged.

All of that said, if you're comfortable with it...
The tubes you bought, were they both 6V6's or was it a set for a Fender Champ (one 6V6, 1 5Y3)
The tube that won't light up, is it one of the two larger tubes, and does it have any markings on it?
Could we get a photo of the amp, indicating which tube isn't lighting up? (a lot easier than trying to describe it)

Could be as simple as the filament in the 5Y3 blowing, which would mean the other tubes won't get any B+ (high voltage) but will still glow (the heaters/filaments run on a separate low voltage supply.)
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Old 21st February 2012, 04:53 PM   #5
kevinkr is offline kevinkr  United States
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Per forum policy this thread belongs in Instruments & Amplifiers. Moved..
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