cj pv2 transformer running hot

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Auriian
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cj pv2 transformer running hot

Post by Auriian »

Hello! I'm new to the site and just pick up my first cj piece ! I'm up in Wisconsin and I have some electronics know how and back ground... anybody remember 'salon one audio' I do.
Well this preamp sounds lovely. The pv2a preamp with black knobs gets a bit warm with the power tranny only putting out 193v and 58v. I suspect caps are dry or ?? Any suggestions out there ? Any recomendations on types of caps to use?
Ray
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Re: cj pv2 transformer running hot

Post by Ray »

I see we have a schematic here on the site, that should help. Is the PV2 dramatically different than the 2A?

Quick glance at the schematic shows pretty straight forward design. Seems like it would be a fun re-build project.
If the thing sounds nice, no hum, noise/buzz, it might just be normal for the tranny to run quite warm. Good luck with it!
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Auriian
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Re: cj pv2 transformer running hot

Post by Auriian »

Tried the download and my phone ain't got the juice to open it. I'll have to check the schematics on a desktop PC... ya the preamp sounds pretty darn good. This site is cool.
Ian Millar
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Re: cj pv2 transformer running hot

Post by Ian Millar »

According to the schematic (which does not appear to be original), the power supply tranny has only a single primary winding which means that there is no means of adjustment for different countries, so that counts out the possibility of user error on that front. It does not count out the possibility of your mains voltage being higher than nominal however. Even with no load, the transformer supplies a voltage, and will get warm due to internal losses. Internal losses = heat and noise. If the core is saturated as a result of over-voltage on the supply side (maximum flux density occurs with no load and the circuit load can ony reduce it) there may be too much heat. C-J transformers are marginally specified devices and high supply voltage could well be the problem. The transformer might be knackered from age too.
Auriian
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Re: cj pv2 transformer running hot

Post by Auriian »

Haven't messed with it yet other than checking the voltages. Input from wall was OK 117-120vac. The output v stamped on the tranny says 320 and 15.75vdc but measures 193 and 58v with only the power plugged in. I can see some discolored 2.2mf250v cap ends next to a ecc81. The Motorola runs pretty hot too. Would bad caps crap the output voltage of the tranny?
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Ian Millar
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Re: cj pv2 transformer running hot

Post by Ian Millar »

Edit. The so-called PV-2 schematic in the download ZIP is a ring-in. It shows 4 tubes only and is the same as the other ring-in for a PV-3! Admin: get it right. Do not share misinformation. :shock:

So take the following as though the schematic were correct which it is not. I discovered it after typing.

...

Please be extremely careful. These are high and lethal voltages. If you want to measure voltage across any two points, connect the probes with the amplifier turned off and disconnected from the wall outet. Stand back, then turn on and obverve your DMM without touching! The unloaded (i.e. tubes removed) DC voltage across C3 would typically be about the AC voltage across that secondary winding times sqrt2 less about 1V. Forget R6. It's just a voltage dropper for that LED. This DC reading would drop as tubes are added to the sockets whereupon and their heaters draw current. This is a "linear" or "unregulated" supply. The transformer should NOT have a dc voltage written on it. A transformer can only provide AC. Unless your DMM is "true RMS" it won't give very meaningful readings. The "Motorola"? I assume you mean the T-03 with the fins around it. This is a fixed bias supply regulator circuit pass transistor and is supposed to run hot. A regulated bias supply drops an input DC (across C2a) to a fixed level that is not affexted by load. The amount of voltage drop determines the amount of heat put off by the heatsink. That string of Zeners and the other transistor and even the resistors will also emit heat. Do not touch the T-03 package. Its case is not at ground potential!

There is probably nothing wrong with that white PP cap with the browned end (all of mine in the Premier Eight look like that) and it would not cause the transformer to run hotter. They all go like that just by electrotstically attracting pollutants. They are very robust. If it were faulty you would hear a problem in the sound.

Remember that transformers must emit heat to work - that EI style might be around 80% efficient (guess) so 20% must radiate as heat and vibration. If you have an IR thermometer you could roughly measure it (point at the dark areas). I would expect it to be quite normal to be 10 degrees C or so above ambient.

Your amp looks well kept. I see there are two black wires around the body of the tranny. Assuming these are NOT Teflon (would be slippery) they look as though they have not seen excessive heat.

If the amp is working maybe there's no problem. The elecrolytic caps look OK. When they go bad, the end caps can bulge like a dome. Yours look flat.

Edit: The only thing that looks suspect in your photo to me is at bottom centre. I can see three slots (of 4) for the 3N253 monolythic bridge rectifier, but there are no legs sticking through (maybe they do but th photo doesn't show). And why is that electro (I guess C3) sitting right there like that on top of it? Strange but I've seen far more ridiculous things in C-J gear.

Also: There is no reason that that preamp would sound any worse than even the most expensive of the current offerings. It looks nice and simple (well apart from the silly regulated supply that doesn't need all those parts).
Auriian
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Re: cj pv2 transformer running hot

Post by Auriian »

I hear you on the voltages I tend to keep the other hand in my pocket while snooping around under the hood and hey thanks for your input/help Id rather not replace anything if I don't have to!
When I first hooked it up I thought it was sounding slightly off balance with greater volume to the right but it seemed to balance out to normal (may have been that Santana song) I guess I'll run it and see how it goes nothing that can't be fixed later and yes this thing is worth hanging onto and fixing it is very good sounding! Thanks again.
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Auriian
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Re: cj pv2 transformer running hot

Post by Auriian »

Bottom pic. Ill run it but I do think it gets a but warmer than it should be.... ill try pushing some air past it
Ian Millar
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Re: cj pv2 transformer running hot

Post by Ian Millar »

That imbalance might be just the old valves warming up. I see they are old Sovteks and Siemens, so they may be a bit long in the tooth. Maybe try to find some Syvanias or something. Tired valves take longer to "come up" on emission tests too.

OK seems there may have been a production run change there. It uses a different type of bridge rectifier than the one that the PCB was originally designed for. Have you got an air compressor? If so you could blow a lot of that dust out. Else use a soft paint brush and blow. Also, that twisted pair of black wires should not wrap around the body of the tramsformer! It could be forming a partial "shorted turn". Now that could cause heat.
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