Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Papa Jim on January 25, 2019, 08:43:30 am

Title: Picking an output and power tranny. Need help.
Post by: Papa Jim on January 25, 2019, 08:43:30 am

If anyone knows the part no.'s or could help me pick a power and output tranny by looking at the below schematic, it would be highly appreciated. I have had success building working amps, but I am definitely  not so much the technical guru to design something. Thanks

Title: Re: Picking an output and power tranny. Need help.
Post by: SILVERGUN on January 25, 2019, 08:53:44 am

Your schematic pic didn't come out so good...try this:
https://el34world.com/charts/Schematics/files/_miscellaneous/Guytronics_gilmore_jr.pdf

Since there are no voltages spec'd, you're gonna have to do a little more research to see if there's anymore info out there.

The Mercury Magnetics transformer numbers are listed on the schematic. You could contact MM and see what the specs are.....

Title: Re: Picking an output and power tranny. Need help.
Post by: Papa Jim on January 25, 2019, 09:04:40 am

Wow. Thanks.  I will contact them.

Title: Re: Picking an output and power tranny. Need help.
Post by: jjasilli on January 25, 2019, 09:45:57 am

https://www.scribd.com/document/250217890/Mallory-150-Gilmore-Jr-Manual-Rev-4-Dual-Primary-MM-PT


The BOM shows Trannies as custom from Mercury Magnetics.  Maybe contact them directly.  Or checkout a similar amp @ ax84.com and use those trannies.

Title: Re: Picking an output and power tranny. Need help.
Post by: Papa Jim on January 25, 2019, 10:12:26 am

Yep I have emailed them. We'll see what they say. That's a great suggestion about finding a similar amp. Thanks. I actually built and have a 2 watt 4-4-Studio amp from AX84. I could borrow the tranny's possibly from it if they are compatible.

Title: Re: Picking an output and power tranny. Need help.
Post by: jjasilli on January 25, 2019, 11:29:27 am

Yes, not sure of your particular schematic.  A PP amp should have a PP OT.  An SE amp should have an SE OT.  PP vs SE OT's are different creatures for technical reasons.  Otherwise, spec'ing a tranny is Voltage & Current.  The PT should provide the desired voltage, at the current it's expected to handle.  The actual current and desired voltage are important, because trannies are poor at "voltage regulation".  So, if less actual current is drawn than the tranny is spec'd for, then the secondary voltage will be higher than spec, and vice-versa.

Title: Re: Picking an output and power tranny. Need help.
Post by: Papa Jim on January 25, 2019, 12:25:36 pm

I don't understand. Does the schematic have mistakes in it. I don't know enough about it to know for sure. As far as I can tell it is wired like a pp.

Title: Re: Picking an output and power tranny. Need help.
Post by: sluckey on January 25, 2019, 06:05:52 pm

It is a self split push pull amp so the OT has to be PP. The schematic is correct. The signal is applied to the top grid. The bottom tube gets it's input on the cathode via the cathodes being tied together. Notice the bottom tube grid is grounded. So the plate signals will be out of phase and do the push/pull action just like any other 'normal' PP amp.

Title: Re: Picking an output and power tranny. Need help.
Post by: Papa Jim on January 25, 2019, 06:22:21 pm

Thanks @sluckey.  I looked through my stuff today and I have everything for this amp except the transformers. Gonna do some reading about how to select them just in case the ones on the schematic are not available.