Tel-ray Supernova

[muttomatic]

Hello!

New to the forum and, of course, I have a question. Recently  acquired the above mentioned amp and I do love it! But, I recently gigged with it and, wouldn't you know it, it died right in the middle of the set! Has power and a fairly substantial hum. And that's about it. Nothing comes through!

Power transistor perhaps?

Any help would be greatly appreciated.

Mutt

[teemuk]

Power transistor perhaps?

Perhaps. Trying to guess what's wrong is pretty futile. Just open it up, do a visual inspection and start probing.

Any help would be greatly appreciated.

Besides fixing the obvious fault, an amp as old as that will require a thorough overhaul and renewal of dried electrolytic caps, drifted components, worn potentiometers and switches etc. If you don't have them yet, you can find very poor schematics from the Tel-Ray page http://www.geocities.com/tel_ray/supernova.html. I don't know how accurate they are and they definitely seem to have some inconsistensies and missing parts. Those are still likely the best ones you'll find from Internet. You may have better chances trying to scetch one out by yourself.

It's an interesting amplifier and an item with historical value. Hopefully you'll get it fixed.

[muttomatic]

Opened it up and there doesn't seem to be any obvious smoked or melted components. I used to work on Airport Radars of the same era technology so the insides aren't completely foreign to me.

There's a daughter board that holds the power transistors and a few other components( you're right that schematic leaves a lot to be desired). There is a molex connector that passes the input and the output to their respective areas. Disconnect it and there is zero hum, so I at least know that the transformer is good to go. I think I'll start at the power transistors and work my way back from there.

I was just hoping that maybe someone here had dealt with one in the past, since they are rather rare birds and so little info is available.

I love the old ss amps. I also have a '71 Kustom 150 head and matching cabinet.

[muttomatic]

Anyone have any leads for a modern equivelant to an MMPS U57 transistor? Can't find anything anywhere!

[tonyharker]

Google MPSU57, or visit www.datasheet4u.com and search for the datasheet.

[muttomatic]

Well, it ain't the power section. Replaced the power transistors, and no change. Taped off the input from the signal section to the power section and quiet as could be. Now I guess we'll try the ol' half split method!

Broke one of MPSU57s moving the amp around... those things are damn hard to find and expensive! Fortunately I found a few at a local surplus shop!

Gonna keep plugging away at the old thing.

P.S. Just noticed that the boards all say "Sano". This amp appears to be the same thing as the Sano 1000R Combo Amp. No schematics for that guy either.

[muttomatic]

Correction... it ain't the signal section... Gotta be in the power section somewhere. Without signal to the power section it managed to smoke the speaker. Good thing it was one I didn't use anymore. Electrons are fun!

[muttomatic]

Finally found my multimeter. Looks like I'm reading 43VDC at the speaker connection! That ain't right...

[muttomatic]

Finally got around to poking around in this thing again. I was looking at the schematic...not that it helps much... and thought that maybe one of the transistors in the power section is bridging some of the existing voltages together incorrectly. So, I started pulling transistors until the 43VDC went away. Wound up being a 2n3645 that I pulled that got rid of the nasty DC voltage. Percieved output volume was way under half the normal volume of this amp. Not convinced that the transistor is actually bad. Doesn't read a short anywhere with the MM. There are a couple diodes on the board that appear to be the same but measure quite differently. One measures like a complete open in one direction(good!). The other... not so much...

[J M Fahey]

Dear Muttomatic: ¿+43VDC on the speaker output?  = 99%: Q4, 5, or 6 shorted. 5 %:R16 open. You can replace your expensive MPSU57 by a cheap Tip30 or BD140 depending on where you live.

[muttomatic]

I believe the 2n3645 is one of those transistors you mentioned... hard to tell... the board and the schematic don't really seem to correlate most of the time. Looking for a 2n3645 replacement now.

[muttomatic]

Looks like a 2905a is a replacement. Going to pick some up today.

[muttomatic]

Popped in the 2n2905a and the voltage dropped to just under 42V...then something popped and the voltage jumped up to 48V and settled back to 43V. I assume the new transistor popped. Everything else reads normal. Can't find any shorted resistors on the power board.... back to the drawing board...

[teemuk]

Do you limit the circuit's current when you test the performed repairs? If not then you need to do that.

[muttomatic]

What would be your suggestion on limitting the current? I always test it with a speaker connected and the volumes turned all the way down. Should I put in a shunt or something somewhere?

Thanks