Newbie - Broken Valve amp help!!

[bloodtypw]

Hi All,

Thanks for taking the time to look at my post.

I have a hand built (not by me) valve amp which I have been building an enclosure for. During the build I clumsily dropped the amp and seem to have broken one of the transformers.
The Transformer appears to be the following model:

Telefunken Netz-Transformator

Bv.40-5112.065-12 Bv/Pv

I cannot find a like for like replacement so was wondering if anyone knew what it's modern equivalent would be, if any?

Any help very gratefully received! Would love to get it working so I can fit it in it's housing.

Cheers
Ben

 

[JonSnell Electronic]

I can see no damage. Where is it broken? Can you repair it?

 

[bloodtypw]

Hi JohnSnell

Sorry, that photo was just of the makers name etc. The damage is on the other side. You can see in the photo here that it has split (I think). Not sure if it can be repaired as I don't know enough about it, sorry!
Would be great to know if it can be repaired or if you think it's ok. I haven't fired it up as I was concerned about what might happen because of this.

Thanks so much for looking!

Cheers
Ben

 

[pageboy]

Do you have a light bulb current limiter? If not, you should, or if you don't know what it is for sure you can google it and find how to make one. They're simple. You can use such a device to turn the amp on and see what happens without hurting anything. If the light bulb lights up brightly then the transformer must have shorted. If the light bulb only barely lights up it should be okay.

 

[cbdb]

The gap, minimizing it, is a huge thing with transformers. You've increased this gap a large amount, I doubt it will put out as much power as it used to, and it might make lots of noise now. And that's if you haven't damaged the windings. Can you take it back to the builder? Has anything else been damaged?

 

[mcandmar]

I remember seeing those transformers listed on eBay so it may be possible to find another one. Also if you can work out which winding's are being used you should be able to find a suitable replacement elsewhere.

 

[Welcome]

It's not split. That thing is called an EI transformer, due to how it looks/is built (although the middle line in the E is covered up and cannot be seen). You're thinking the I part has broken off, when in reality, it was designed like that. It's just a little crooked.

 

[KatieandDad]

The Es and Is should be touching to form an 8, the gap is severely detrimental to the operation of the transformer.

Was this transformer welded into an 8 and the weld has given way ?

If you can get the Es and Is out of the transformer bobbin and separate them you could then rebuild the core alternating the Es and Is so that they overlap. (ie half the Is are at one end and the other half are at the other end).

 

[DF96]

It would be very unusual for a power transformer to be built in that way, with E and I laminations separated. Normal for an output transformer. Very puzzling. Are you sure that is the same transformer?

 

[Parafeed813]

Don't worry about the transformer, it doesn't look defective.
Apparently the builder made the mistake of not putting supports on the top to keep the 'E' and 'I's together, so it's not your fault either.
I have seen more Telefunken trannies that have all the 'E's on the same side of the bobbin with a block of 'I's on the other side. It saves time in production, therefore money.
Put some metal strips with holes for the mounting bolts on the top to fix it tight together (or find a matching hood).
As said, best thing is to take all lams out and restack properly by alternating the 'E's from both sides. For power trannies you often see them stacked in groups of three if the lams are thin. (three left, on top of that three from the right, op top of that three from the left, etc).

 

[knockbill]

I'd squeeze it together with a clamp and make four metal strips to extend from bolt to bolt on each side of the stacks, and tighten it under the existing nuts, while its clamped in place, that would hold it together,, then start the amp back up on a DBT as was previously mentioned...

 

[bloodtypw]

Hi All,

thanks so much for all your responses - so much to take in.

Great to know that it might not be defective and that clamping the E and I back together as described may solve the issue. I have managed to source a replacement one (a reclaimed Telefunken) which should arrive in the next few days. I plan to swap it out and test it.
If it works, great but if it doesn't I'll try and fix the original as per the info you have all kindly shared. I'm new to all of this so I can't tell you how grateful I am to get the advice from you all.

Couple of questions if thats ok?:

When the replacement arrives, can I de-solder the old one and replace it then fire it up or are there any things I should be aware of?

The other question is, what's a DBT?

Thanks again everyone.

Cheers
Ben

 

[bloodtypw]

Hi All,
The other question is, what's a DBT?

Dim Bulb Tester!

Sorry, should have worked that out earlier.

I'll have to do a google search to work out how to use one though.

Cheers
Ben

 

[bloodtypw]

Sorry all, can I ask a couple more questions ? I've made myself a dim bulb tester ready to test the amp.
When I bought the amp the builder said I should never fire it up without the speaker connected. Is this the same for testing? Should I connect the speaker before testing? Also, should the valves be in place too?
Thanks in advance everyone.
Cheers, Ben

 

[bloodtypw]

I've just tried turning on the amp via a Dim Bulb Tester and although the bulb didn't light up, the amp made an alarming loud buzzing sound. This is without speakers and valves attached.

Any ideas?

Thanks in advance

 

[GoatGuy]

Yes: replace the transformer. All the clamping in the world isn't going to fix the buzz (and might make it worse).

Well… not exactly true. IF you were to get a little 1 hr epoxy and carefully swipe it on both surfaces in the gap before vise/clamping , then clamp and let harden, the noise ought to go away. You might have to do "both sides" though! This has worked for me.

GoatGuy

 

[bloodtypw]

Yes: replace the transformer. All the clamping in the world isn't going to fix the buzz (and might make it worse).

Well… not exactly true. IF you were to get a little 1 hr epoxy and carefully swipe it on both surfaces in the gap before vise/clamping , then clamp and let harden, the noise ought to go away. You might have to do "both sides" though! This has worked for me.

GoatGuy

Thanks Goat Guy. I have a replacement on order so probably best bet is for me to switch it out to be on the safe side.

 

[bloodtypw]

Hi GoatGuy. As a test I clamped the two sides together and that reduced the buzz to a loudish hum. I reckon the replacement is probably the way to go.

 

[bloodtypw]

This appears to be an SE guitar amp, please confirm and I will move it to the proper place.

I see a solid state bridge rectifier, it is more likely that one of the diodes has shorted UNLESS the ballast lamp (sorry not dim bulb) does not light with no tubes installed and a known good fuse in the fuse holder. (check fuse before running test)

Hi KevinKr, thanks for your message. I can confirm it's an SE amp. Apologies if this post is in the wrong place.

The light on the chassis lights and the fuse has not blown. I don't know if this tells us anything? How would I test the diodes?

Thanks again.

 

[bloodtypw]

my post from last thread: The gap, minimizing it, is a huge thing with transformers. You've increased this gap a large amount, I doubt it will put out as much power as it used to, and it might make lots of noise now. And that's if you haven't damaged the windings. Can you take it back to the builder? Has anything else been damaged?


believe me now?

Hi cbdb, I meant no offense re your last post. I've just been trying to explore all avenues. The gap is indeed large and makes a huge amount of noise. I temporarily clamped it and it reduced the noise to a noticeable hum. I have a Telefunken replacement on order but I'm interested in mcandmar's thoughts about an alternate replacement - hopefully a modern one.

I can't see anything else that has been damaged but I'm feeling my way through it and learning very slowly as to how to check what is working and what isn't. As far as I can see, only the transformer is damaged, although kevinkr thought the diodes may have shorted too. So if I get a steer on how to test them, I'll check those too.

I bought the amp quite a while ago from someone who posts on Amp Garage forums but can't find his contact details unfortunately - although I am still searching.

Thanks again for your help, I really appreciate it.