Hammond PT with Fixed Bias 6V6's

[Geezer]

  Hoffman Amplifiers
    > Tube Amp Building - Tweaks - Repairs
        > Hammond PT with Fixed Bias 6V6's      
 
<< Prev Topic | Next Topic >>  
Author  Comment  
eddiejg
Senior tube assistant
Posts: 249
(3/17/04 6:05 pm)
 Hammond PT with Fixed Bias 6V6's
--------------------------------------------------------------------------------
 I am just building my 1st couple of fixed bias amps.
I've used the Hammond 270 series (275-0-275) for both EL84's & 6V6's in cathode bias.
I just did a fixed bias amp using EL84's & the 270DX tranny.
I have around 370 volts on the plates.
Will I get a similar voltage on the plates of 6V6's with the same 270DX?
Or should I use a 272 series (300-0-300) for 6V6's?
I'm looking to get 400+/- using JJ 6V6's.
-Ed
 
GroundhogKen
Forum Moderator
Posts: 2327
(3/17/04 6:56 pm)
 Re: Hammond PT with Fixed Bias 6V6's
--------------------------------------------------------------------------------
 I have a dual 6v6 amp with a Hammond 270EX. ( 300-0-300 125mA )

With a 5Y3 I get about 335 on the plates,
with a 5AR4 I get about 370,
with no tubes installed I get about 420v.

You might just barely get 400 if you use a solid state rectifier.

With a tube rectifier you'll need a 300-0-300 transformer to get 400v.

Hope that helps.

Those JJ 6v6 tubes are built like tanks. I use them in my BFDR, but I bet I could plug 'em into my Super Reverb with no problem. They're a little bigger than the typical straight bottle 6v6 tubes that I'm used to. I think JJ used the same glass that they use for their GZ34 rectifier.


Ken
 
eddiejg
Senior tube assistant
Posts: 250
(3/17/04 9:11 pm)
 Re: Hammond PT with Fixed Bias 6V6's
--------------------------------------------------------------------------------
 Ken-
The answer man strikes again- thanks!
I'm building a Pignose G40V with the JJ 6V6's (more like a G25V).
I should get the correct voltages with the 272DX & a GZ34.
I really like those JJ's.
Do you know if they are officially rated for more plate dissipation than the normal 6V6?
-Ed
 
GroundhogKen
Forum Moderator
Posts: 2328
(3/18/04 8:29 am)
 Re: Hammond PT with Fixed Bias 6V6's
--------------------------------------------------------------------------------
 The JJ 6v6 spec's courtesy of Uncle Spot:


Re: jj6v6 - 'spec sheet' from the NAMM show...

A.F. beam pentode
Base: octal
Uf = 6.3 V
If = ca 0,5 A

Typical characteristic: class A1
single tube Push-pull
Ua = 250 V 250 V
Ug2 = 250 V 250 V
Ug1 = -12,5 V -15 V
Ia = 45 mA 70 mA
Ig2 = 5 mA 13 mA
Ra = 50 kohm -
Ra-a - 10 kohm
N = 4,5 W 10 W

Limiting values:
Triode Pentode
Ua = 450 V 500 V
Ug2 = 450 V 450 V
Wa = 10 W 14 W

Grid No 1 circuit resistence
Fixed Bias 0,1 M ohm 0,1 M ohm
Self Bias 0,5 M ohm 0,5 M ohm

Capacitances:
Cg1 = 9 pF
Ca = 8,5 pF
Ca/g1 = 0,7 pF
 
eddiejg
Senior tube assistant
Posts: 251
(3/18/04 9:55 am)
 Re: Hammond PT with Fixed Bias 6V6's
--------------------------------------------------------------------------------
 Ken-
Thanks.
You probably could pop them into your super.
And they will definitely work for me with the amp I'm building.
I think I'm going to use the 272DX & I'm going to try to use diodes instead of the GZ34, although I might put a socket in so I can switch between the GZ34 & a rectifier replacement socket.
The Pignose has 416 volts on the plates & I'm guessing that I'll get ~400 with the GZ34 & ~430 with the diode.
So, I'll have to play around with that & also the dropping resistors to get the correct voltages on the preamp tubes.
-Ed
 
 
 << Prev Topic | Next Topic >>

 

 Topic Commands
 Click to receive email notification of replies
  
jump to:  Tube Amp Building - Tweaks - Repairs (New)New Product Suggestions (New)Praises - Complaints - Suggestions (New)Buy - Sell- Trade (New)Archives (New)    
 

- Hoffman Amplifiers - Tube Amp Building - Tweaks - Repairs - Hoffman Amplifiers -



Powered By ezboard® Ver. 7.32
Copyright ©1999-2005 ezboard, Inc.