Need a power transformer for a JTM50, Marstran, Merren or Classictone

[wpaulvogel]

Burned one of the HT windings in my Marstran 1202-118 with a rectifier short. Need a replacement

[Roe]

classictone is fine

[wpaulvogel]

That’s what I’m considering but I’m going to have to tear down all the wiring because classictone has flying leads. Guess it’ll be the cost for saving $50. Is Marstran still in business?

[Roe]

Yes I think and hope so. Ask Brian

[wpaulvogel]

He replied. I’m going to open up the transformer myself. I pushed on the paper around the terminals and saw a spark. It might be possible for me to get to the open winding and repair it. We’ll see. If I can it’ll save me $164.

[wpaulvogel]

Opened up the wrap, sucked the solder off the 5v terminals and the ht high, ht low and ct. pulled up the terminal strip and found the ht high broken right at the terminal. Was able to pull up a little more winding wire to reach the terminal. He had left it long. Put all the leads back through the terminal strip and soldered everything back. Tested for continuity, good. Powered it up through the current limiter, good. Plugged straight up and got 335-300-0-300-335. Good. Hooked up rectifier wires to ht high terminals. Current limiter again, good. Plugged in. Get 326 on both sides and 402 +\- dc on the plates. Ran it up with a signal and get 41 watts clean and 70+ wide open.
I’m pretty excited about this. Time will tell if it’s permanent but for now it’s working. That was through a GZ34 tube. I’m waiting for the octal base to show up so I can make the SS rectifier. I’m going to use 4 or 6 1N4007 vs the pair that were in the CE Distribution plug-in. Y’all be careful if you have one of those plugins. I pretty sure they can’t handle the peak inverse voltage.

[Roe]

Opened up the wrap, sucked the solder off the 5v terminals and the ht high, ht low and ct. pulled up the terminal strip and found the ht high broken right at the terminal. Was able to pull up a little more winding wire to reach the terminal. He had left it long. Put all the leads back through the terminal strip and soldered everything back. Tested for continuity, good. Powered it up through the current limiter, good. Plugged straight up and got 335-300-0-300-335. Good. Hooked up rectifier wires to ht high terminals. Current limiter again, good. Plugged in. Get 326 on both sides and 402 +\- dc on the plates. Ran it up with a signal and get 41 watts clean and 70+ wide open.
I’m pretty excited about this. Time will tell if it’s permanent but for now it’s working. That was through a GZ34 tube. I’m waiting for the octal base to show up so I can make the SS rectifier. I’m going to use 4 or 6 1N4007 vs the pair that were in the CE Distribution plug-in. Y’all be careful if you have one of those plugins. I pretty sure they can’t handle the peak inverse voltage.

excellent news. I should try the same on a marstran 1203-80 with broken/shorted bias supply

[wpaulvogel]

Something else I found is that the original builder has the white neutral run to the mains fuse. I’m going to change it to the black 120 volt lead. I’m not sure why they have done this, it might have something to do with the fuse not protecting the circuit when the diode failed. Looks to me like if something shorted to the chassis that the neutral might not see the current and therefore not protect. If it only had a two wire plug it would work but like it should be, it’s a three wire earthed connection.

[wpaulvogel]

I got the SS plugin built last night and did some more checking. Getting 442 volts with no power tubes. Tubes in and biased to 30mA have 429 volts on the plates. Get 28.5 volts clean output through 16 ohm dummy load. 50 watts! Got 40 volts across the meter full boar. Is that something anyone else has seen? That’s 100 watts!! Makes me think about putting the GZ34 back in.

[Tony Bones]

The old Mullard datasheet says 54W with 400V B+, so there must be something wrong with your amp.

[wpaulvogel]

Damn defective Tung-Sol EL-34B tubes.