For the Amp Techs - Trannies

[ToneMonkey]

A bloke over on the Patrick Eggle forum has helped me out a few times and asked the following question over there.  As there's a few Amp Pros (yeah, you know who you are  :lol:) on here, I thought I'd post it to see if I can help him out.

Cheers dudes  PDT_003


Can anyone help me with some advice regarding power transformers.
A mate of mine has the opportunity to buy (at a very good price) a used VHT Fifty Twelve combo with a suspected power transformer failure. The guy who’s selling it is a professional session player as well as playing in his own band, so the VHT is well gigged, although it is in excellent condition cosmetically inside and out, he bought it new about 5 years ago.
 What I would like to know is: - What do I (or rather my pal) need to know in order to be able to order a replacement from a UK manufacturer or distributer. The only numbers on both power and output transformers are 16421F and 16422B both dated 2003, but these numbers don’t seem to get me anywhere when searching the web for replacements. The amp has switching for 4, 8, and 16 ohms impedance. Could he for example use a transformer designed for a 50 watt Marshall or Fender or would it have to be a specific one for the VHT? 

[Twinfan]

It's pretty much down to the power valves in it and therefore the voltage they need.  If they're two EL34s in the VHT, then a 50w Marshall spec tranny should do the trick.

I think...

[HTH AMPS]

It all depends really.  If the PT is centre-tapped on the HT winding, then you'll certainly need a CT'd transformer.  Similarly, if the HT winding has no CT, then you'll need a PT without a CT that is spec'd for the correct voltage.

Does it have a bias winding? - maybe it has a separate winding to power the relays?

If you can get a schematic of it, I'll be able to confirm these things and recommend something suitable.

Have you contacted VHT to enquire about a replacement PT? (the UK distributor should be able to supply these).  I would always recommend this route.

[jpfamps]

Firstly let's assume it is the transformer (and I would want a second opinion on this before I order an expensive part like the mains transformer).

In my experience you are best getting the correct replacement transformer and fitting that.

Trying to fit a differnet transformer can be a real pain, and involve some metal work.

Using the correct transformer will also help preserve the value of the amp.

I would be surprised if VHT didn't supply replacement transformers, although they may have a policy f nbot supplying transformers to emembers of the general public only approved repair shops (Marshal;l have taken this policy, although at the moment they don't have any transformers......).