Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on July 08, 2014, 04:28:40 am

Title: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: kagliostro on July 08, 2014, 04:28:40 am: I've 4 or 6 (don't remember well) not matched 1625 so I've think to draw the Power Section of the Stendal 25L15 with this tubes

I need your councils about the value of resistors I've used in my schematic

also I would like to know if the choice of a 5,000ohm primary is OK for the OT (with Plates and G2 at 270v DC)

I do my choice looking to the attached 807 Datasheet (Look to page #5 for 17.5W output 2% THD)

Have you councils about a better OT primary impedance and Plate and G2 voltages ?

Thanks

K
Title: Re: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: kagliostro on July 09, 2014, 06:36:02 am: I've just find this two schematics

and I'm always more unsure about B+ and the correct OT primary impedance, also considering the use of 1625 tubes instead of 807 tubes :rolleyes:

:w2: :w2: :w2:

K
Title: Re: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: PRR on July 09, 2014, 11:30:46 pm: > Plates and G2 at 270v DC

I think that is very low for the classic Standels.

The parts and some detailing come out of the Heathkit "Willamson" power amplifier kit (or something very much like it; everybody sold an "American Williamson" kit). IIRC the B+ was above 400V.

Resistor and OT values depend on the B+.
Title: Re: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: kagliostro on July 10, 2014, 01:57:01 am: Quote
Resistor and OT values depend on the B+

You are right

---

But what about the schematics I've find that are "labeled" Standel, are genuine or fake ?

can I use those values to suppose which was B+ ?

Thanks

Franco
Title: Re: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: jazbo8 on July 10, 2014, 02:09:09 am: Seriously doubt those are the original schematics - could be good copies made from the original though... Isn't the "secret sauce" in the preamp anyway? :icon_biggrin:
Title: Re: Standel 25L15 with 1625 - are this values correct for power amp section ?
Post by: kagliostro on July 10, 2014, 02:23:49 am: Quote
Isn't the "secret sauce" in the preamp anyway?

I believe so

I'm just trying to configure correctly the power section (as seems this isn't so secret as the preamp is)

as preamp section I'm looking with interest to DummyLoad's prototype http://el34world.com/Forum/index.php?topic=17282.0 (http://el34world.com/Forum/index.php?topic=17282.0)

Franco