6b4g pushpull build!newbie

[tubo]

hey fellas!!!! i am a tube newbie....i can read a schematic and i am contemplating on building my first tube amp! a pushpull 6b4g by ralph powers on the meta gizmo site! i will be using the eico st-70 irons, i am not sure if it will work because it's primary z is 6.6k and the schematic says 5k! i am only asuuming that it is 6.6 k basing it on a fisher ot that is 6.6k using 7591 tube!

thanks in advance!!!!

[AndreasS]

Hi,

I've build a 6B4G push-pull amplifier using the Hammond 1650G with 6,6 kOhm primary, it works.

http://www.jogis-roehrenbude.de/Lese...B4G/6B4GPP.htm

Regards
Andreas

[tubo]

thanks, andreas!!!!!! i will post an update regarding my build.....btw. do you have a schematic for the amp that youve built? ty

[tubo]

andreas,

saw your schem.....nice amp!!!btw how does it sound?

[Eli Duttman]

Originally posted by tubo
hey fellas!!!! i am a tube newbie....i can read a schematic and i am contemplating on building my first tube amp! a pushpull 6b4g by ralph powers on the meta gizmo site! i will be using the eico st-70 irons, i am not sure if it will work because it's primary z is 6.6k and the schematic says 5k! i am only asuuming that it is 6.6 k basing it on a fisher ot that is 6.6k using 7591 tube!

thanks in advance!!!!

Dude,

You have 7591 O/P "iron". Build with 7591s. A Class "A" PP pair of triode wired 7591s is good for about 10 W.

A nice thing about the 7591 is that it's as easy to drive as "12" W. tubes. Fisher and Scott took considerable advantage of that fact. What Fisher and Scott did, you can do too.

You said this will be your 1st tube build. Have you already built a preamp? IMO, a possibility you should consider is building a higher powered variant of "El Cheapo". No preamp is needed.

[tubo]

thanks eli..

yeah i was also thinking about the el cheapo too... probably in a couple of weeks when i come back in the good ol usa ill start building the el cheapo when i scrounge up enough parts to build it!!!btw are you a member of the hawrhorne audio forum?i was browsing on that site earlier and i thought i saw your uname down there...thanks again

[Eli Duttman]

btw are you a member of the hawrhorne audio forum?

I occasionally "play" in Eddie Vaughn's "sandbox" over on the Hawthorne "board.

[jrdmedford]

Andreas! I've noticed you are using a Hammond 124E as a CT
grid choke to drive the 6B4G grids! Do you have any measurements
on how well this device supports signal level and frequency extension?
The 124E is certainly a bargain compared to the Lundahl 1660 or
the MQ EXO-170 if it do the job as a grid choke!

Have you considered the Hammond 124B, this is the 124E with
49% nickel alloy.

-- Jim

[AndreasS]

Originally posted by jrdmedford
Andreas! I've noticed you are using a Hammond 124E as a CT
grid choke to drive the 6B4G grids! Do you have any measurements
on how well this device supports signal level and frequency extension?
The 124E is certainly a bargain compared to the Lundahl 1660 or
the MQ EXO-170 if it do the job as a grid choke!

Have you considered the Hammond 124B, this is the 124E with
49% nickel alloy.

-- Jim

Hi Jim,

yes, the 124E is a simple interstage transformer. In my amplifier it is connected as a differential anode choke for the driver: 1st secondary, the primary and 2nd secondary are seriell connected.

Difficulties are from the interwinding capacitances in the higher frequencies (about 12500 Hz); the short feedback path (6 dB) from the anode of the drivers to the anode of the phase inverter solves this problem.

Best regards
Andreas

[AndreasS]

Originally posted by jrdmedford
...Have you considered the Hammond 124B, this is the 124E with
49% nickel alloy...

Yes, but the 124B is to small and a seriell c.t. connection of the c.t. 10 kOhm and c.t. 90 kOhm windings isn't possible. I use this transformer as a 4:1 autotransformer (paraphase) in a preamplifier.

Regards
Andreas