First Vintage Tube Amp...VOM

[ScaleAutoArt]

The seller called me today and said the pre amp isn't 100% functional so we agreed on a lower price. So now I will have to troubleshoot. It was working fine prior to removing it from the console so something got knackered. Hopefully its a simple fix.

 

[ScaleAutoArt]

What's that little red thingie?

Pilot light connection. Which the seller is sending along. I have the manual and will post the diagrams.

 

[Dandy]

The face plate of that preamp looks so pretty, and has the 12AX7s, I would definitely try to include it in a final build. If possible some pictures along the way so we can enjoy the fun. The bright colors of the cabling under the hood look as if the amp was made last week.

 

[ScaleAutoArt]

The face plate of that preamp looks so pretty, and has the 12AX7s, I would definitely try to include it in a final build. If possible some pictures along the way so we can enjoy the fun. The bright colors of the cabling under the hood look as if the amp was made last week.

Yes...it looks factory fresh...amazing. I definitely want to keep it together. It has real charm. I am thinking of a nice enclosure for the pre amp with the amp mounted on top partially exposed and incorporating the "pilot light".

Here are some schematics and system layout:

 

[ScaleAutoArt]

The amp arrived today is good shape. Pretty darn clean internally...lots of those little ceramic/epoxy coated brownish red discs. Do these need to be replaced?

I will post photos in the next few days...perhaps someone can point to the critical caps to replace...but on the surface they look really good.

 

[Dandy]

In the power amp, apart from the can, there are only two ceramic discs that I can see. The latter are probably good, so don't replace till you've got it all working. The three part can should probably be replaced, but you could try reforming it by bringing it up slowly. That's worth trying if the previous owner had the amp running regularly before selling.

There are obviously more caps in the preamp unit. Can we see a pic of the under- or inside of that? I'm still learning about preamp upgrades, but those in the signal path, if ceramic, could be replaced. But, they are likely to be good, so again don't replace yet. Assuming you start with the Aux input, caps that I think most affect the signal quality are: C3, C8, C9, C12, C13, C14 (this is for one channel; the same with those in the other channel).

But, I would just check out/replace that can cap and then try it out.

 

[ScaleAutoArt]

I took some detail shots yesterday. I will need to do some overall Monday.

When you say can...are you referring to the can on top? I am new at this.

The PO had it powered up...I powered it up and one power tube was dead so one channel worked fine but then the sound cut out suddenly and I got a nasty squeal that elevated so I shut it down. I suspect one of the pre amp tubes ? I did order new tubes for the whole setup just to start fresh.

 

[gadget73]

Looks like it has a bunch of ceramic disc capacitors. Those are usually electrically OK. I'd leave them for the moment and worry about the black tubular ones.

 

[knockbill]

Nice sized OPT's on that guy, and the preamp matches it,,, I'd probably build a case for the amp and pre to fit in, and repair/recap as needed,,,
It would make a nice little integrated, especially if you add a phono section...
Good luck with it...

Regards,
John

 

[ScaleAutoArt]

Nice sized OPT's on that guy, and the preamp matches it,,, I'd probably build a case for the amp and pre to fit in, and repair/recap as needed,,,
It would make a nice little integrated, especially if you add a phono section...
Good luck with it...

Regards,
John

That's the master plan :thmbsp:

 

[Dandy]

I took some detail shots yesterday. I will need to do some overall Monday.

When you say can...are you referring to the can on top? I am new at this.

The can is the multi-section electrolytic capacitors (in one can) on top. These smooth the high voltage after the rectifier for the power supply. Yours has a 60uf, 40uf and 20uf cap in the one can. These often dry out if not much used. But might be okay if the PO used it regularly. Normal procedure is to replace them. You can look out for a replacement can, or replace with similar single electrolytics. Note these must be installed with the correct polarity.

As gadget73 says, the problem you report is more likely to be caused by the black tubular caps, like those in your picture. Replace with the same values and same or higher voltage. These are non-polar.

 

[Schmidlapper]

Since you know this unit has been powered up recently the capacitors in the "can" now have the potential of a fatal dose of electricity stored in them. I don't know your experience level working with tube gear, but regardless it can't be stated enough, follow rigorous safety precautions. If you don't know what they are then defiantly take a step back and do some studying on it. This unit looks well made and designed so you will be pleasantly surprised how enjoyable they do sound. For me the research aspect was half of the the enjoyment of my recent restoration project on a different chassis pull. It re-ignighted my interest in audio equipment after a very long break. Have fun with the VOM.

 

[loonze]

I had one similar to this

:tresbon::thmbsp:

 

[ScaleAutoArt]

Since you know this unit has been powered up recently the capacitors in the "can" now have the potential of a fatal dose of electricity stored in them. I don't know your experience level working with tube gear, but regardless it can't be stated enough, follow rigorous safety precautions. If you don't know what they are then defiantly take a step back and do some studying on it. This unit looks well made and designed so you will be pleasantly surprised how enjoyable they do sound. For me the research aspect was half of the the enjoyment of my recent restoration project on a different chassis pull. It re-ignighted my interest in audio equipment after a very long break. Have fun with the VOM.

Yes...I understand. I thought 24 hours would be sufficient to discharge. Is this correct?

 

[knockbill]

Check em with a meter,,, and ground them thru a resistor, 100ohm works, just to be sure...

Regards,
John

 

[ScaleAutoArt]

Since I have only done very simple work so far I feel more comfortable having a service tech do the recap on this and test it. Found a local shop so I will bring it there tomorrow. The fun part will be cleaning it up and making a nice box for it.

 

[Dandy]

Great to have a local tech look at it. Ask him (or her) to point out what they have done and to keep any parts that they replace, so you know for next time. There will be a next time...

 

[ScaleAutoArt]

Well...my local tech went over it with a fine tooth comb and aside from some loose connections [which were the source of the noise] it is in very good shape. He tells me nothing needs to be replaced at this time. He had it playing this afternoon when I walked in.

It's sounds great!

 

[Dandy]

Sometimes there just isn't a problem! Nice result.

 

[ScaleAutoArt]

Set this up with my turntable in my workshop today.
At first it chirps and hums a bit...and has somewhat distorted sound...but fully warmed up it's a whole different story!