Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rp3703 on July 17, 2021, 12:51:57 pm

Title: Looking for PT candidate for JMP-1watt Clone
Post by: Rp3703 on July 17, 2021, 12:51:57 pm

I am looking at building a JMP-1 watt clone. I found this schematic and have for the most part confirmed it’s accuracy. I plan on using a Hammond 125A for the OT but am having trouble figuring out the PT. The Dragnall puts out 0-200V/ 0-11.5V on the secondary. Does anyone know of a hammond or other manufacturer with something similar or an alternative power amp solution that uses a commonly available PT? Is there an advantage to running the filament supply DC?

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: Willabe on July 17, 2021, 01:40:35 pm

Quote from: Rp3703 on July 17, 2021, 12:51:57 pm

Is there an advantage to running the filament supply DC?

DC heaters can actually at times be nosier.   

I like to use dcv elevated heaters with a humdinger pot. (I use 70 to 80dcv.) 

Read this;

http://www.valvewizard.co.uk/heater.html (http://www.valvewizard.co.uk/heater.html)

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: Rp3703 on July 17, 2021, 03:37:33 pm

Are DC filaments just a PCB thing?

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: sluckey on July 17, 2021, 04:00:21 pm

no

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: Rp3703 on July 17, 2021, 04:15:11 pm

But other than reducing hum, they do not contribute to the tone of an amp, right? So going with regular AC heaters would be fine if implemented correctly.

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: thetragichero on July 17, 2021, 04:36:40 pm

i built a ~4w single-ended el84 plexi clone using the hammond 269ex transformer (probably most known for the ax84 high octane) i had lying around and it worked well for me

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: Willabe on July 17, 2021, 06:16:42 pm

Quote from: Rp3703 on July 17, 2021, 04:15:11 pm

But other than reducing hum, they do not contribute to the tone of an amp, right? So going with regular AC heaters would be fine if implemented correctly.

They do not change the tone of the amp. Very few guitar amps have dc heaters, and their quiet.   

Title: Re: Looking for PT candidate for JMP-1watt Clone
Post by: Rp3703 on July 17, 2021, 07:38:20 pm

Thanks Willabe, I think I’ll try AC filaments and see what happens.
Tragichero, I actually have a spare 269EX from a Firefly I built, I’ll give that a try and see how that goes as well. Thanks.