Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Marc on March 17, 2022, 08:12:35 am

Title: Power transformer "custom" wiring
Post by: Marc on March 17, 2022, 08:12:35 am

Hello EL34 World Forum,

I built a working custom version of the Ampeg HB15.
https://ampeg.com/support/files/Schematics/H%20Series/HB-15%20(Heritage)/AMPEG%20HERITAGE%20B-15%202010%20SCHEMATIC%20AMENDED%202.7.2012.pdf (https://ampeg.com/support/files/Schematics/H%20Series/HB-15%20(Heritage)/AMPEG%20HERITAGE%20B-15%202010%20SCHEMATIC%20AMENDED%202.7.2012.pdf)

I have a question about the wiring of the power transformer,
on a 230VAC 50Hz electricity network (in fact it varies between 231 to 238 at least), is it safe to wire the Hammond 373BX in 240VAC mode?

• 700VCT will be lowered which is what I want because B+ is around 480VDC and sometimes more
• 6.3VCT will be in the tolerable range
• 5VCT is not a problem (solid state rectifier is used)

Documentation:

• https://www.hammfg.com/fr/part/373bx (https://www.hammfg.com/fr/part/373bx)
• • https://www.hammfg.com/files/parts/pdf/373BX.pdf (https://www.hammfg.com/files/parts/pdf/373BX.pdf)
     
• https://www.hammfg.com/fr/electronics/transformers/classic/300 (https://www.hammfg.com/fr/electronics/transformers/classic/300)
• • https://www.hammfg.com/files/products/300/230v-primary.png (https://www.hammfg.com/files/products/300/230v-primary.png)
  • https://www.hammfg.com/files/products/300/300s-240.gif (https://www.hammfg.com/files/products/300/300s-240.gif)

To me it should be OK.
Are there any considerations / harmful things to take into account?

Title: Re: Power transformer "custom" wiring
Post by: kagliostro on March 17, 2022, 08:21:56 am

Tollerance in the order of 15 - 20% (components & voltages) are acceptable in tube amps


Franco

Title: Re: Power transformer "custom" wiring
Post by: Marc on March 23, 2022, 08:12:57 am

Thanks for the advice.

I switched from 230 to 240VAC wiring mode and it works well.
The 6.3VCT is between 6.35 to 6.42VAC.
The B+ is now around 450VDC allowing me to use more 6L6GC models.