pignose keeps blowing up power transformers

It is a good deal. Thanks for the link!

I have a bare 220V (240V?) Variac that I bought for $25 a while back, and I need to mount it on a board or something and put a plug on it. Makes that $45 look pretty good.

Hey, no problem! :)

Those variacs *are* made in China, and I was a bit worried about what the quality was going to be like, but I needn't have worried...the one I received is very nice. The integrated meter and fusing is also a big plus, which you can't find on US-made/branded units that sell for under $200.

The only other thing that I added was to build a little current-limiting circuit to plug the unit into, which simply consists of a box with an outlet to plug the variac into, a power cord, a SPDT switch, a 100-watt halogen lamp, and a pilot-light jewel lens. All it really is, is a 100-watt halogen lamp and a switch to alternately either insert the halogen lamp in series with the hot leg going from the power cord to the outlet, or connect the hot leg straight through. The more current that's drawn, the brighter the jewel will be.

This will limit inrush and total current nicely, and is especially useful for firing up those questionable/unknown garage-sale finds and the like for the first time. Also for initial power-ups of home-built amps and repaired amps, especially in cases where new filter caps have been installed. I've found this to be very, very handy for saving repeatedly-blown fuses and stress to the variacs' contact arm brush and the amp under test. Note that this little box can be useful all by itself, even without a variac, although I'd recommend adding a fuseholder + fuse if it will be used alone.

>EDIT: I thought I'd better add that you should use only a metal enclosure, and drill a few small holes for heat dissipation, as halogen lamps get *really* hot!<

Cheers!

Strat

That sounds like a good arrangement. Maybe I'll build something like that with the bare Variac I have.

When you find it, note that it's basically identical to the Marshall JCM 800 2204 "Super Lead Fifty." But built with the cheapest possible components. :D

Oh, cool .... Now, does it have a real Marshall like tone, then? I've only ever seen the picture on the pignose website, I don't think the write up suggested to me that it was a "British Amp" clone ..

(sounds like it could be a good project amp. Just wait for things to blow and fix with better components :-) )

No, they've never suggested anything Marshally about it. Yet it's nearly identical in its circuitry. Download the schematics and compare for yourself. And I do think there's a considerable similarity in how it sounds, though you'll seldom hear the Marshall played through a single 10" speaker in a tiny, open backed cabinet. Plug the Piggy into a 4x12 cab, and you'll hear the kinship much better. (The Piggy is biased very "cold" so it can safely get away with no bias adjustment. Most Marshall players nowadays like to bias them as "hot" as they can get away with. That also influences its characteristics.)

Ricochet, maybe they didn't want Marshall to notice the similarity :-)

Interesting that the tubes are biased "cold", but the heater is run at a higher voltage...I guess they were not then thinking about tube life when they set up the bias.

They were thinking only of low cost, which is aided by simplicity. They went a step too far when (I believe) they tried to use a single power transformer to run on Japanese and US house current.

Hey folks, I bought and installed a pair of Sovtek 6l6 tubes, and measured the new voltage to the tube heaters to be 6.65 volts. Do you think this needs to be lowered? Also, I opened up the two dead power transformers that I have, and found a blown fuseable resistor in the windings of the primary coils on both of them. I removed the fuses from the circuit, and put the transformers back together. The primarys on these transformers now measure the correct impedance again. Are these transformers ok to use? I'm just thinking about if it blows another transformer, i'll have 2 spairs.
I was also thinking that maybe the whole reason i'm having this problem is because the fuseable resistors are made to handle the Japanese 100v and not the US 120v. If so, then this one will go eventually too, and i'd like to be able to use the repaired transformers if possible because they're so expensive. Does this sound reasonable?
Thanks once again for the help!

6.65V's a little high, but not unreasonable. I'd probably leave it alone.

My Piggie was bought in 2001, and possibly its transformer was an anomaly anyway. Just as EVJs have gone through several stages of evolution since I bought mine, the G40V you buy today may be rather different from mine.

However, if this thing's blown fusible links in two transformers, it's drawing too much current for some reason. I'd suspect the bias circuit's not working right, unless it was just a defective tube or tubes drawing too much current.

Doggone power fuse ought to blow before the link in the transformer. Maybe you ought to go down a step on the fuse capacity?

hmmm possibly...
This amp was purchased as one of those "scratch and dent" items in early 2004. When I first bought it, the back panel was dented in, and the amp had some sort of connection problem(I think), where it would turn off after playing for about 15 minutes. The problem eventually went away on its own.
At this point i'm really thinking that the old Chinese tubes were screwed up, and drawing too much current, and thats why the transformers were blowing. Perhaps they were screwy and also caused the initial problem with the amp when I first purchased it. The amp is now a lot less noisy with the Sovtek tubes in the pre and power amp, plus the chinese tubes always had blue in them, which I know isn't supposed to be there. I've been planning on moving the electronics into a head with a small fan on the side(a project that was put on hold by the transformer, as well as school.) Perhaps I'll just do that and then watch everything real carefully.
as a side note, do you think those transformers with the link removed are useable in the future?

Yes, blue on the inside of the glass is supposed to be there. It's a healthy sign. Here's one site explaining this normal phenomenon: http://members.aol.com/larrysb/blue_glow.html

However, many power tubes contain a little too much residual air, and any tube can leak some in and become gassy or "soft." When this happens, ionized air molecules will pull electrons out of the grid and reduce the bias, letting more plate current flow, which heats up the tube so more air is released from the internal surfaces, it gets ionized, and the whole thing snowballs till something burns up or a fuse blows. Common mode of failure for power tubes.

Well, one thing is for sure, the amp is working better than ever with these new tubes. It used to be very microphonic...now even if I whack the top of the amp while playing it doesn't make a sound. There is also far less other noise and the amp sounds way better. I think those Chinese tubes were damaged from the beginning. The blue I was talking about wasn't the normal stuff, but instead a large blue spot that would rapidly fluctuate between on and off. This would correspond with the amp working or not. There were numerous other strange noises that this amp made over the years, although none of them lasted too long. Like I said this is the first time the amp seems to be working at 100%, and i'm very pleased.

Yeah, the old 6L6s were likely the culprit.

Hey by the way thanks soo much for all of your help ricochet!

You're welcome.