Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: phsyconoodler on January 27, 2012, 10:59:20 am

Title: how much voltage can a reverb transformer handle?
Post by: phsyconoodler on January 27, 2012, 10:59:20 am

I just build a nice one channel vibrolux and it sounds awesome.But it killed the reverb transformer after a couple of weeks use.I used a Super Reverb PT with diode rectifier and it has 500v on the plates.I adjusted the dropping string so the preamp voltages aren't too high but the reverb + is hovering at 495v.It's on the same node as the screens.Is it too high?
  The amp blew fuses and it was definitely the brand new Hammond reverb tranny.I replaced it and all is working again.
 The reverb is deadly good on this amp.Wonder if it was just a faulty tranny?
Any insight?

Title: Re: how much voltage can a reverb transformer handle?
Post by: tubenit on January 27, 2012, 11:23:00 am

I don't know the limits to a Reverb Trannie?  Having said that I typically have had fewer than 400v on the reverb trannie.

You may already know this but you can add a resistor between B+ and a reverb trannie to lower the voltage.

I first learned this by direct communication with Hammond about 6 (?) yrs ago.  They sent me a hand drawn schematic showing a resistor there.

And I don't remember where, but I have seen amp schematics that used a resistor there also.

With respect, Tubenit

Title: Re: how much voltage can a reverb transformer handle?
Post by: phsyconoodler on January 27, 2012, 11:54:45 am

I'm going to put a 100k resistor in there.I don't want to kill another tranny.
Thanks Tubenit! Appreciate the input!
  You should write a book with a chapter called: "A conversation with Hammond"

 Sorry,it just popped into my head. :laugh:

Title: Re: how much voltage can a reverb transformer handle?
Post by: phsyconoodler on January 27, 2012, 01:13:28 pm

I've built several amps with 500+ volts and the reverb tranny's are still alive after 5 years.Maybe Hammond's aren't as robust?I used mojo ones in those amps.
  Hmmm.....the plot thickens.

Title: Re: how much voltage can a reverb transformer handle?
Post by: EL34 on January 27, 2012, 05:24:29 pm

I don't think it about the voltage, it is about the current flow/wattage.

Title: Re: how much voltage can a reverb transformer handle?
Post by: Tiny_Daddy on January 28, 2012, 10:01:48 am

I have seen a shorting problem with several brand-unknown reverb transformers where the wire openings don't align with the wires and the insulation was pinched resulting in latent failure. Check your new parts before installing. I have had to remove some covers and enlarge the holes.