Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: j_bruce on May 04, 2020, 01:21:42 pm

Title: how to choose a power transformer?
Post by: j_bruce on May 04, 2020, 01:21:42 pm

So my Gretsch 6159 project has a bad transformer and I cannot find any specs on the original to try to match it up.

My best contender is a Classic Tone 40-18060 https://www.tubedepot.com/products/classictone-power-transformer-40-18060 (https://www.tubedepot.com/products/classictone-power-transformer-40-18060)
which is listed as the one used in the Supro Thunderbolt. I think this might be a good match based on both using two 6L6s and being from the same company and time frame.

What is the typical way to determine what transformer specs are needed?

Thanks for any help,
Jerry

Title: Re: how to choose a power transformer?
Post by: Latole on May 04, 2020, 03:03:16 pm

https://el34world.com/Forum/index.php?topic=23281.0

https://el34world.com/Forum/index.php?topic=16664.0

Title: Re: how to choose a power transformer?
Post by: sluckey on May 04, 2020, 03:13:00 pm

See my comments in your other thread about this amp.

Title: Re: how to choose a power transformer?
Post by: shooter on May 04, 2020, 03:18:01 pm

+1

Quote

typical way to determine what transformer specs are needed

many ways, I start;
add up all the tubes filament current from datasheet, .3A+.6A+....
a schematic with PA plate VDC is GREAT thing, if not;
PA tube datasheet, "typical operations" pushpull, or SE
find plate volts, current zero signal X number of PA tubes
call it 400vdc plate, (.04A X 2 tubes) = 80mA + ~ (4mA X 3 small tubes) == 102mA
decide type of rectifier, say full wave bridge;
so 400/1.414 ~280 VAC @ ~~120mA with call it 3A filament winding

OR
find any amp close with same PA tubes and about the same small tubes that you can find a part# for and go the easy route  :icon_biggrin:

Title: Re: how to choose a power transformer?
Post by: j_bruce on May 04, 2020, 04:27:03 pm

Quote from: Latole on May 04, 2020, 03:03:16 pm

https://el34world.com/Forum/index.php?topic=16664.0

That taught me what I needed to know. I really should do a better search before posting!

Shooter's typical operations approach matches it well.

400v/1.414 ~280v preferred
2 6L6 + 4 12ax7 = 140 + 16 = 156mA

heaters  2*.9 + 4*.3 =3A

This one looks like a good fit: http://www.classictone.net/40-18103.pdf (http://www.classictone.net/40-18103.pdf)

Thanks
Jerry

Cheers,
Jerry

Title: Re: how to choose a power transformer?
Post by: Latole on May 05, 2020, 03:26:43 am

Quote from: j_bruce on May 04, 2020, 04:27:03 pm

Quote from: Latole on May 04, 2020, 03:03:16 pm

https://el34world.com/Forum/index.php?topic=16664.0

That taught me what I needed to know. I really should do a better search before posting!

 
Cheers,
Jerry

Google have all the answer...most of the time :laugh: