Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jamesedmunda on August 22, 2020, 08:45:38 am

Title: Power Transformer for Laub Engeering Model 26
Post by: jamesedmunda on August 22, 2020, 08:45:38 am

I need a power transformer for a Laub Engeering model 26. Kind of a Magnatone 260 clone.
It looks like a Fender Hot Rod transformer would work.
 Doesa anyone see any problems, here's the specs.

Fender Original Hot Rod Deluxe Power Transformer. Equivalent to #036958.

Specifications Primary 120 VAC @ 60 Hz (Black - White) Secondary 1 (Red - Red) 495 VDC unloaded, 440 VDC @ 65.7 mA DC, 388 VDC @ 200 mA DC Secondary 2 (Brown - Brown) 53.6 VAC @ 1.58 A AC Secondary 3 (Green - Green) 6.6 VAC @ 3.75 A AC

Fender part number: 003-6958-000
 Mojotone has one with 4 amps on the Heater winding, would that be a better fit.

Fender Original Hot Rod Deluxe Power Transformer. Equivalent to #036958.


 Thanks again James

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: vampwizzard on August 22, 2020, 11:10:00 am

You may be a little high on the B+ if you dont use the 48V winding otherwise it appears you have enough current available for the tubes.

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: Latole on August 22, 2020, 11:26:24 am

Did you check how much current tubes's heater need ?

Transformer specs are 6.6V at 3.75 amps

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: vampwizzard on August 22, 2020, 12:40:36 pm

looks like those 6CG7's take .6A per tube. You're looking at ~4A of heater current. 

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: DummyLoad on August 22, 2020, 02:55:58 pm

another option.

https://www.edcorusa.com/xpwr021 (https://www.edcorusa.com/xpwr021)

--pete

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: jamesedmunda on August 22, 2020, 03:06:33 pm

Thanks for the reply Pete.
 Do you think the B++ is high enough the schematic shows 390 volts while the Edcor  transformer is only showing 290volts.
 Thanks James

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: sluckey on August 22, 2020, 03:44:27 pm

Quote from: jamesedmunda on August 22, 2020, 03:06:33 pm

Thanks for the reply Pete.
 Do you think the B++ is high enough the schematic shows 390 volts while the Edcor  transformer is only showing 290volts.
 Thanks James

290VAC will make about 410VDC unloaded. Probably be just about right with load. But, you've been looking at laydown type transformers. Can you use a standup type transformer?

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: PRR on August 22, 2020, 05:03:19 pm

> schematic shows 390 volts while the Edcor  transformer is only showing 290volts.

Schem is DC Volts, Edcor sells you AC Volts. Not the same. Counting on thumbs, 400V DC might be 282V AC. Or what DL said. More VAC if it was a tube rectifier, but it isn't.

A "5F6a Bassman" PT will work out to around 400VDC (with different rectifier connection!) but is probably over-kill (more current than you need).

Title: Re: Power Transformer for Laub Engeering Model 26
Post by: jamesedmunda on August 23, 2020, 04:39:18 pm

Thanks Guys,
 I've ordered the Edcor.
James