Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: proaudioguy on February 18, 2024, 11:13:53 pm

Title: Up for grabs.....
Post by: proaudioguy on February 18, 2024, 11:13:53 pm: 3 RCA 12AU7
4 Sylvania 12AU7
1 GE 12AU7
3 RCA 12BH7

Send me a small flat rate box shipping label (self addressed and pre-paid) and I’ll send them out. Please verify you are selected cause I don’t want 18 people buying a shipping label.
Title: Re: Up for grabs.....
Post by: scstill on February 20, 2024, 11:58:28 pm: Thanks for the tubes, Label sent

I missed that they are 12v heaters
But the datasheet says I can use them at 6.3v with parallel heaters
So with a little change in wiring could be used as 6au7 :-)
The 12BH7 seems similar specs to the 12au7
Title: Re: Up for grabs.....
Post by: WimWalther on February 21, 2024, 12:37:04 am: Quote from: scstill on February 20, 2024, 11:58:28 pm
I missed that they are 12v heaters
But the datasheet says I can use them at 6.3v with parallel heaters

All of these tubes have a bifrucated heater - it's a 12V heater across pins 4 & 5 with a center tap connected to pin 9.

They can be run at 12.6V across 4 & 5, or at 6.3V across 4+5 & 9. It's this latter connection that you see in probably 95% of cases, since 6.3V is a standard heater voltage for many common power tubes.

So you're fine either way.
Title: Re: Up for grabs.....
Post by: scstill on February 24, 2024, 06:25:08 pm: Awesome all tubes work and will be put into service soon.
Found out the 12bh7 is a big version of the 12au7 (thread in EL34)...
Title: Re: Up for grabs.....
Post by: AlNewman on February 24, 2024, 08:37:46 pm: I have a Marshall DSL5 with 12BH7 PP power section.
It's not may favourite sounding amp, but I think that's more in the pre amp. It is loud, and probably could be tweaked to be pretty nice. Anyhow, cool tube, and lots of bang for a single socket.
Title: Re: Up for grabs.....
Post by: WimWalther on February 24, 2024, 08:40:56 pm: Quote from: scstill on February 24, 2024, 06:25:08 pm
Found out the 12bh7 is a big version of the 12au7 (thread in EL34)...

I've always thought of the 6CG7 / 6FQ7 as being in that role. Though, the 6CG7 is also much like a Noval 6SN7.
Title: Re: Up for grabs.....
Post by: scstill on February 26, 2024, 06:52:02 pm: I have a small amp build that uses 12au7 in SE parallel plate.
I just swapped the 12bh7 and like it,
BH seems louder than the AU even though specs call out same amplification factor.
The BH does need twice the heater current, fortunately the PT has just enough.
https://stillampd.com/silvertone-deluxe-micro-04

In specs, I do not see much difference between the BH and AU
except the heater current and 2.75w plate dissipation for AU and 3.5w for BH