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Scott 340a HT voltage off transformer

CJVx

CJVx

AK Subscriber
Subscriber
Hello all, i just purchased a Scott 340 receiver without the original power transformer. My best estimate is that the secondary windings will produce 350VAC P-P judging by the schematic stating that there is 470VDC right after the pair of GZ34's (assuiming roughly 10V drop through each tube). Would any proud owners of this piece of equipment be so kind as to pull their rectifiers and take an AC voltage measurement at pins 4 of each socket? this will tell me the unloaded voltage coming out of the secondaries for the high voltage. I am looking into Heyboer Transformers to build me a new transformer, but this is important information that they need! Also any suggestions on what current capabilities would be needed on this set of secondary windings would be appreciated.
 
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Do you know what the original part number of the transformer is and if it is the same as a 340B? I have a B on the bench (well, OK, dining room table... shh...) right now and I have all the leads coming out of the transformers disconnected, so if you can verify it is the same I could very easily take measurements. I'm ASSuming that mine is OK, although the original fault with the unit was a dead short, so if my measurements don't make sense I might need one as well! If that turns out to be the case I would be happy to send the unit to Heyboer for post mortem as this would help us both. Just need confirmation that they're the same!

Edit: the 340B xfmr is a TR15-2.

per this link http://www.fmamradios.com/AmpSpecs.html yours is a TR15. I don't know if there are any meaningful differences, maybe someone can help?
 
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As an aside, I believe but have not confirmed that the "138...." is a serial number. Can anyone confirm/deny?
 
Thanks for the replies. Looking at the 340B schematic, it shows the transformer splitting the high voltage winding into two separate parts, so i dont think that would be the same as the 340 transformer. I have been zooming in on internet pictures that have the transformer # legible and they all have been saying TR-15, so that has to be the model number, still cant find any specs on it.
 
What is the problem with the amp? I don't think there is anything wrong with your power transformer. Even a single shorted winding will draw excess current and get hot and/or smoke. If it is behaving, it's probably ok. Transformer problems do happen but are rare in my experience, and from what I have read on the forums in the past 10 years, is also pretty rare.

You realize that between the two high voltage leads minus the CT that you are going to have double the AC. Make sure your meter is set on AC when doing AC measurements. DC when doing DC measurements after the rectifier(s).

If you are getting low DC, one or both of your rectifier tubes could be bad.
 
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OP I believe doesn't have it at all.

If you're asking about my 340B, it'll pop a fuse as soon as you plug it in, and the power switch is blasted to heck. I'm currently waiting for a) the Brown Santa to bring me my Mouser order and b) Hayseed to come back from what I assume is a well deserved vacation so I can order new can caps. I troubleshot it as far as determining that I'm pretty sure all the iron is good but I'm just going to recap this rather than repair it because it seems like a good idea. I'll replace the germanium rectifier for sure, and I ordered diodes for the HV rectifier just in case that's bad too. I'm guessing the problem was either the HV rectifier or a shorted can cap associated with that circuit. I did determine that at least the winding of the PT that connects to the tuner is good as I can power it up with the others disconnected, and I'm getting voltage readings on the other windings too now that they're lifted.
 
A Sherlock Holmes mentality can certainly deduce certain problems, but I shudder at posts where people just guess at the problems and shotgun the thing hoping a recap or diode replacement will cure the problem.

A simple meter will tell you instantly where you short is. With an ohm meter, it will tell you if your capacitor, transformer, or diode/rectifier is shorted. 2 seconds will tell.
 
I understand what you're saying but I feel justified in ordering all the questionable stuff because as I said it's a dead short in the HV section... and I want to be able to trust this thing. Makes sense to me to just replace all the 'lytics and the coupling caps and having the other possible parts on hand rather than finding the one component that's causing the issue and then still not being able to trust the thing if I walk out of the room with it playing...
 
Best to have things fused then. I never worry about my stuff even with original 'lytics as everything I own is fused.

I can understand Nagel's point of view also but I must keep reminding myself that nearly every old radio that's been refurbed or rebuilt, still have their original power transformers in them. I'd sure hate to see you put in new caps or something and have them blow up or smoke because of something else that went unchecked.

I personally don't live my life as though something is going to happen, it worked for me today, and tomorrow may never come! :beerchug:
 
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Oh yeah there is a main fuse, but I've heard that if certain caps fail they can take out your output tubes and/or transformers, and they're relatively inexpensive in the grand scheme of things.
 
Yeah it's pretty rare but does happen. People have their stories. I have only come across maybe one amp out of hundreds that I can remember over 30 years that had a shorted filter capacitor run unchecked. I remember plugging it in and smoke filling the room. I don't remember the brand but the power transformer was ok and so were the outputs but maybe I got lucky as I didn't know its history or abuse. Oh, and it didn't have a fuse! :mad:

I have come across many amps and receivers in the past where the main filter capacitor was shorted, but they were all fused and the fuses (thank goodness) did their jobs. :thumbsup:
 
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