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Help with a new 45 SET amp....

Looks like it's going to be an all around $hitty weekend...

So, here's what I found....

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Not a whole lot in the way of tell tale signs....:no:


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Still NADA. I even scraped off some of the coating on the coil wires to get a better contact. Also, I checked the unused wire....:thumbsdn:

Also an open circuit.....:sigh:

So now what?

How much would it cost to get this rewound?

How much for a replacement set of OPT's?

I have a set of spare iron lying around somewhere.

What might the necessary specs be?

Is this going to be worth the trouble....:tears:
 

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dunno what a replacement set of OPT's would cost, nor the cost of having yours repaired, but I'd guess an amp and tubes like that one would cost $1000 or more on ebay... I'd look into repairing it!
 
analog addict said:
So, here's what I found....

<snip pics>

Not a whole lot in the way of tell tale signs....:no:




Still NADA. I even scraped off some of the coating on the coil wires to get a better contact. Also, I checked the unused wire....:thumbsdn:

Also an open circuit.....:sigh:

So now what?

How much would it cost to get this rewound?

How much for a replacement set of OPT's?

I have a set of spare iron lying around somewhere.

What might the necessary specs be?

Is this going to be worth the trouble....:tears:
Click to expand...

Too bad about the OPT. Rewinding will probably be an expensive option. I would expect at least $100-200 if you have it done professionally. If you do choose this route, a competent rewinder will provide you an OPT that largely matches your existing good one. If you replace the bad OPT with something other than an exact copy, you'll probably experience a sonic difference betw channels because the OPT is a very large part of the sound of amp like this.

Which leads to the second option: replace both OPTs with current production avail from any number of sources. Assuming this amp follows typical design practice, you'll need a primary resistance of ~4.5-5K ohms with secondary taps to your needs. You can also measure the pri and sec of the good OPT to get present impedance specs. Power rating will be 2W or greater. Suppliers that come to mind are One Electron, Hammond and Electraprint and there are others. Expect to pay $100+ depending on brand and specs.

Obviously, you've now entered the realm of DIY and are no longer into the plug-n-play mode so you may want to engage some local assistance if you choose a transformer transplant.

Or maybe Barry+Sue can offer you another option if DIY isn't what you want.

EDIT:

After re-examining your teardown pics, it's fairly obvious that the OPTs are repurposed push-pull OPTS (red/brown/blue leads is the std code for PP plate leads). If so, your only practical choices are to either get a rewind or replace both OPTs...assuming of course that you won't be able to locate an old stock replacement OPT identical to the ones you now have.
 
Steve O said:
Or maybe Barry+Sue can offer you another option if DIY isn't what you want.
Click to expand...

Yep, put it back together and box it up for a trip back to Hampton. No need to go any further if you are not comfortable with the repair options noted.

I'll send it to my tech and get her up and running if not too much of a hassle. Otherwise, I will put it up for sale as is and see what happens.
 
if you decide to replace the OPTs, one option is the magnequest RH40, which are $100 each. I just got a couple for a 45 SET build. I don't know how they sound yet since I haven't built the amp, but they certainly have a good reputation and the "robin hood" series is a much more economical option than other high end pieces.

the other thing you could do is send me those 45 tubes, as my project is stalled until i can source me a good pair!

good luck!
 
OK I'll bite...

Took a quick look around, and couldn't find a thread on how to measure the Primary impedance.

Anyone wanna guide me through it?...:scratch2:
 
Sure, Take your variac and tickle the primary with some AC voltage (say 40v), then measure the voltage at the secondary (8ohm) tap. Take the 40 and divide it by what you read at the secondary. Take that number and square it (multiply it by itself), then multiply by 8 (from the 8 ohm secondary). That will give you the primary Z, which I would guess to be somewhere between 3 to 5K.
 
OK, let me get this right....

There are two leads from the OPT to the speakers. These are the secondaries.

There are two leads from the OPT to the circuit, one to the 45 tube B+, the other to one of the + terminals of some of the caps. These are my primaries, correct?

Can I apply the 40 VAC to the primaries while the working OPT is still in circuit, or do I need to remove it?...:scratch2:
 
analog addict said:
There are two leads from the OPT to the speakers. These are the secondaries.

There are two leads from the OPT to the circuit, one to the 45 tube B+, the other to one of the + terminals of some of the caps. These are my primaries, correct?

Can I apply the 40 VAC to the primaries while the working OPT is still in circuit, or do I need to remove it?...:scratch2:
Click to expand...

Yep, the speaker wires are the secondaries, and the wire on the 45 and the one on the caps, are the primary. I don't see any problem doing it in place. Try it and see what you come up with.
 
jaymanaa said:
These are nice and can usually be had for 100 or 110 a pair (I've done some buisness with this guy). http://cgi.ebay.com/Pair-5k-Audio-O...14&_trkparms=72:1205|66:2|65:12|39:1|240:1318

He has them in 3K too, so you probably want to test your good one and see what the Pri. Z actually is. That's a bummer for sure, if there's anyway I can help anyone with this, I'm more than happy to.
Click to expand...

jaymanaa said:
Sure, Take your variac and tickle the primary with some AC voltage (say 40v), then measure the voltage at the secondary (8ohm) tap. Take the 40 and divide it by what you read at the secondary. Take that number and square it (multiply it by itself), then multiply by 8 (from the 8 ohm secondary). That will give you the primary Z, which I would guess to be somewhere between 3 to 5K.
Click to expand...

Nice transformers Jay,

And yeah exactly how I check my primary "Z" I even do them straight into the wall. Carefully!

I even have read of 1930's stories of how a filament transformer would be taken apart put back together air gaped and used as a SE Output Transformer so when you do the math for a 6.3 VAC secondary and a 120 VAC primary it works out to a 2.9K primary. A 5 VAC works out to 4.6K primary for an 8 ohm connection.

SET12
 
A Happy Ending....

Just to finish off this thread. I replaced the original OPT's with the Transcendar SE OPT's. Had a screen/50% tap added for a couple of bucks, bringing the total cost of 2 custom US made OPT's to $125 including shipping. A few new mounting holes, a little solder and WOOHOO!!!!!!

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Total cost about $255, including the "new" Westinghouse 5V4G off of E-pray...

Not bad considering what I got out of the bargain...:music::music:..:banana::banana:
 
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