tweed champ kit heartbreak

[wade carlton]

Hello. Brand new to the forum. I recently finished building a
tweed champ kit from stf electronics and after two days of
intense pride and great tone, my amp started making a
very mild crackling noise when I strummed chords. An hour
later, it died completely. Now, when turned up, it makes a
quiet squealing sound and the OT " buzzes". I also noticed a
spark inside the output tube before turning off.
I have been playing through one 8 ohm 25 watt jensen which I
am told is okay, even though the amp wants 4 ohms. Voltages
check out fine on all the tubes and my connections look good-
no arcs between pins on tube sockets or anywhere else-
passive components tight in eyelet board The amp has not
been run without the speaker and the speaker tests out fine. If
the OT is fried, what could have done it? I am pretty newb to
this and have had enough of my own ignorant guesswork.
Anybody wanna have mercy and help me fix this baby?

[Geek]

Hi,

Hopefully your iron isn't fried.

Sounds to me you may have had a lame output tube. What brand was it?

Cheers!

[wade carlton]

It's the electro harmonix 6v6gt that came with the parts kit- which means sovtek with a different label? It would be great if it was the output tube. Would the OT be buzzing? Also, I probed around one of the primaries with a sharpie and noticed that the."mild squealing" diminished and increased in relation to it's vicinity to the nearest signal cap.

[Geek]

Sounds like something "changed" over the two days, it went into ultrasonic oscillation and *poof*.

I had 6V6's that did this on their own in a couple days, because they couldn't handle 430V on them (Sylvania). RCA's could no problem and the amp's been fine since.

I'd triple check your wiring and component layout, then drop in an "expendable" tube if you have one arund and if it's fine for a couple days, replace with J/J or RCA or something a little nicer.

Cheers!

[Hotsauce]

I doubt the OPT is bad. You're hearing something in speaker, so its not blown open. They can blow shorted, but thats less likely.

Ask the kit maker what resistance of windings should be, and check them with meter to be sure.

8 ohm speaker draws less power than 4 ohm.

John C.

[dhuebert]

I have had nothing but trouble from the E-H 6V6s. I wouldn't put them in anything I built. My advice: buy some NOS RCA smoked glass 6V6. I have been using them in the Champs that I build with great success. They have a smoother more bluesy breakup than the E-H and will probably last the life of the amp.

http://cgi.ebay.ca/RCA-6V6-BEAM-POWER-T ... 3f0562f870

As an example of what to buy.

Don

[Geek]

^----- Ya, dat's da vun! -----^

[EWBrown]

The Fender Champ and the Deluxe Tweed amps reaqlly push the 6V6s into another dimension beyond the normal rather "wimpy" ratings for these tubes, and any "lesser" 6V6s will meet a sudden demise under these conditions.

My recently completed Tweed Deluxe clone, I put in all vintage US tubeage, and it is definitely nicer sounding than the J/J and Russian stuff. (which I use during the initial start-up testing, as these are what I would consider "sacrificial" tubes, if one of them gets blown up, no big deal

You're right, ElectroHarmonix is just Sovtek with a fancy label. Otherwise it's the S.O.S...

/ed B in NC

[wade carlton]

Thanks for the kind input everyone. I will eventually get some good NOS 6V6, but right now my attention is sadly on the output tranny, which is definately rooked. What else besides severely mismatched impedence could cause total OT failure?

[EWBrown]

For now, a J/J 6V6S would be perfectly good, these tubes are built more like slightly smaller 6L6GCs and can really take an electrical beating.

The cheap EH 6V6 goes bad, then draws excessive current through the OPT primary. Just enough current to cook the windings, but not burn them out. This situation then "runs away" only getting worse over time - even a few minutes.

This could cause an internal primary, or primary to secondary short, which would only exacerbate the situation.

I'd go with one of the Triode Electronics TF103-48-UL OPTs they are reasonably priced and work very well. These have both 4 and 8 ohm outputs.

Or one of the Edcor GXSE10 or GXSE15 OPTs. 5K primary and 4 or 8 secondary to match your speaker. These have only a single secondary value, 4, 6, or 8 ohms, not tapped like the TF103.

Is this one of the Tube Depot "Champ" kits? Friend of mine asked me if I could build one for him, if he decides to buy one.

/ed B in NC