Tel-ray Supernova

[Artspoke]

Thanks!  So here's what's in there:

4x  22-3773  -  power transistors mounted 2 each on two large aluminum heatsinks
2x  SEN T-73  -  mounted underneath the main power supply board - no heatsink
1x  156-043  -  also mounted underneath the main power supply board - no heatsink

I found an old Sunn schematic that calls out for 22-3773, and lists 2N3773 as an alternate part number, which is easy to find for sale.  It also seems that 156-043 is sparsely available.  But after talking with tech support at Motorola, Onsemiconductor, and Westinghouse, no one has ever heard of any part number resembling SEN T-73.  Any suggestions?

My plan is to replace the four 22-3773's and R14, and hope for the best.  Parts of the schematic (downloaded from the link provided in the thread - thanks) seem to match my Supernova very well, but none of the transistors have part numbers.  Are these three TO-3 packages (2x SEN T-73 and 1x 156-043) as likely to be shorted as the 22-3773's?  Does anyone know their function, or have different part numbers for these?

I'm pulling all of them out now so I can check them for shorts.  I'll report whatever I find.

Thanks,
-James

P.S., I've taken nearly 100 pics of this thing, so if anyone needs a picture of anything, I've likely got it, or would be happy to photograph any part of it from any angle.

[Artspoke]

Sure enough, Collector-Emitter short on one of the four power transistors.  Just ordered 4 new 2N3773's to replace these 22-3773's. . . hope they do the trick!

Is there anything I should be looking for as a potential cause?  I've read pages 84-89 (from the above recommended book) about 10 times, and now I want a DC ammeter, an ACVTM, and a nicer scope (I have a Heathkit from around 1960. . .)

Thanks again for the help - you were dead right.

[Artspoke]

At last - my transistors arrived!  And now it's working deliciously! Thanks!!
The ones that were in there read 22-3773, and my working <3) 2N3773's are well, working well!! 

I can't remember it sounding any different - fantastic dynamics, and completely silent when not playing.  As soon as the oil comes in, I'll fill the cans up (they're supposed to get about a tablespoon each?) and report back.

Now I want to build a custom cabinet for it. . .  The original advertisements hail:

"two-12 inch heavy duty eminence (Altec Lansing optional)"

and then it says:

"150 R.M.S. 425 watts peak power into 2 OHM load"

Is it advisable to run this amplifier into a 2 Ohm load (I'm guessing two parallel 4 Ohm speakers)?  I've been running it through a single 10", 8 Ohm cabinet, and it sounds fine.  What's the safest choice?  If I want a 2-speaker cabinet, what speakers/overall cabinet resistance make the most sense?

Also, I'd like to add a line out to make it possible to record directly to tape.  I've read about cabinet emulators that accept a power amp output and then simulate the non-linear resistance dynamics of a speaker. . . not too concerned about all that!  What I'd like to know is, can I just tap the pre-amped signal someplace and get a line out?  I'd rather not use the amplified signal at all - not even to the speakers sometimes.  Will this hurt the amp (disconnecting the speaker load)?  Is there a special dummy load for old transistor amps?

I thought about just making the input to the spring reverb into a y-cable, and recording that!  Any recommendations on a good spot (if any) to tap the preamped, effected signal, and get it into shape for a nice, juicy, balanced ProTools input?

I'm so glad it's working again - thanks again for the help.

[Artspoke]

Mixed report:


    -  When the oilcan effects are off, I get beautiful, dynamic, noise/distortion-free tone.
    -  The Reverb and Tremolo effects sound great.
    -  I bought a Tektronix 465B oscilloscope, a Lambda triple DC power supply, and a Fluke bench meter.
    -  I built a custom 4-switch foot pedal with parts from Home Depot - works great!



    -  The oilcan effects are noisy.  There is a regular pop, synchronous with the rpm of the Rotating Sound motor, that can be heard even if the Rotating Sound effect is off.  It can be heard when either the delay or the rotating sound effects are on at all, and gets louder as these effects are turned up.

    -  There is some noise that I can hear and see on my scope when the effects are on.  It is (in addition to the cyclical pop) very high frequency, and sounds like static/grounding noise.  I have replaced all of the components on both of the two amp cards mounted to each motor, with no noticeable effect.

    -  The Long Delay setting yields unimpressive results compared to the Short and Multiple settings.  The long delay send wire that comes from the selector switch was broken off.  It looked like the break had happened at the top (backmost looking at the amp), two pins away from the input wire.  There are a few caps and resistors wired into this messy switch - doeas anyone have a hi-res picture of this switch wired properly?  The scematic I have differs from the electronics inside - not sure if it's been modded or if it's just a different version.

I have completely disassembled both motor assemblies, inside and out, and meticulously cleaned everything right down to the screws and washers (used up two toothbrushes, five 00 brass wool pads, a brass brush, a steel brush, and more than 1000 two-sided Q-tips (no joke)).  In fact, in addition to cleaning, resurfacing, and polishing literally everything, I also resoldered every connection in the entire amp.  I replaced the power transistors, all of the electrolytics, the power resistor (which was killed by one of the original(? 22-3773) power transistors that shorted out), and completely restored the hardware, skin, and the crumbling original wooden deck.  She looks like new!  Again, I've got over 150 pics if anyone's interested . . .

In fact, playing through the clean channel, or the effects channel with both the Echo and Rotating Sound effects off, it drives an 8 Ohm 12" or a 4 Ohm 15" beautifully.  This tells me that the preamp and power amp are clean and fine.  All of the components on the can-cards are new, and still test ok taking them out of the circuit.  The insides of the cans were completely disassembled and cleaned, and 20 ml of special-order oilcan oil was added.  I put new belts on.  Could the AC motors just be tired/old and leaking noise?

Anyone have any guesses/ideas/inklings?  I'm out, and really excited to have that "AHA" moment worth 2000 Q-tip swabs.

My last idea is to replace the 2-prong AC plug/wire with a proper, three-prong, grounded set.  There's no harm in doing this is there?

Thanks for all the help, this Supernova may as well have been called the Odyssey!

[joecool85]

I'd start with proper grounding, I think you are right on there.  No damage done by replacing the 2 prong with a 3 prong plug, make sure to ground the chassis with the 3rd prong, it doesn't do any good if the ground wire isn't attached anywhere  :tu: (yes - I've seen people do this)

[gbono]

I believe Temuk is refering to a "light bulb" limiter used on the mains input to limit current in the case of a fault. The circuit consists of wiring a low wattage bulb in series with the amplifier.