Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: crashtm1 on November 29, 2017, 06:28:26 am

Title: 5E8a builds
Post by: crashtm1 on November 29, 2017, 06:28:26 am

Has anyone built a high powered version?
Specifically the 5E8a , not 5f8.
How about with a PPIMV?

Title: Re: 5E8a builds
Post by: centervolume on December 05, 2017, 08:33:57 pm

Yes, I built a 3-12 version 4x5881 twin circuit 5F8-A

Title: Re: 5E8a builds
Post by: crashtm1 on December 31, 2017, 08:12:07 pm

Digging through my stash, I found these two beauties. A Mono tweed bassman PT (340v) and a MM JT4550-G4 (380v).. I've emailed MM for the specs and diagram.
What difference will I see between these two? More power? Tone?

Title: Re: 5E8a builds
Post by: drew on December 31, 2017, 10:22:05 pm

What "high powered" configuration are you contemplating? Both of those PTs are for amps that use a pair, not a quad, of power tubes.


Re: the PPIMV question, http://el34world.com/Forum/index.php?topic=15984.0 may be useful.

Title: Re: 5E8a builds
Post by: crashtm1 on January 01, 2018, 12:32:53 pm

I'm currently building low power tweed twin 5E8a. I had considered dumping the 2 rectifier tubes and converting it to a 4x6L6 amp with SS rectifier. But for now I'm going to stay with the original layout.

Title: Re: 5E8a builds
Post by: crashtm1 on January 02, 2018, 08:30:43 pm

Can someone explain the B+ voltage change notes at the bottom?
Does this mean the B+ changes depending on the rectifier?

Title: Re: 5E8a builds
Post by: sluckey on January 02, 2018, 08:46:46 pm

Quote from: crashtm1 on January 02, 2018, 08:30:43 pm

Can someone explain the B+ voltage change notes at the bottom?
Does this mean the B+ changes depending on the rectifier?

Bottom of what? If you are referencing some schematic post a link so we can see it too.

Title: Re: 5E8a builds
Post by: crashtm1 on January 02, 2018, 10:12:30 pm

Been a long day..

Title: Re: 5E8a builds
Post by: Joel on January 02, 2018, 10:43:31 pm

Tube rectifiers are not as efficient as solid state rectifiers.  So yes, the B+ changes depending on what sort of rectifier device/s you are using.

Title: Re: 5E8a builds
Post by: crashtm1 on January 05, 2018, 05:18:33 am

Solid state.

Title: Re: 5E8a builds
Post by: ac427v on January 05, 2018, 08:06:13 am

If that is a MOJO 752 it would have a solid state rectified B+ of around 500 volts! The 5E8-A schematic shows 400 volts to two 6L6G power tubes. A 5R4GYB tube rectifier would get you a lot closer to the original voltage. I also see that this Twin needs an uncommon (for guitar amp) choke because it must handle the entire high voltage load, not just the preamp tubes and power tube screens. I bet someone on this forum has found a suitable Hammond choke. I think it would be a very sweet amp if you can get close to original voltages.
Craig