Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ledzepp007 on September 20, 2016, 01:29:46 pm

Title: Tweed Overdrive Special Build
Post by: Ledzepp007 on September 20, 2016, 01:29:46 pm

I'm getting ready to embark on a build.

I'm going to gut my 100-watt plexi build and use the chassis, choke, and one of the 50uf/50uf cap cans outta there.

I have a random assortment of left over transformers: a Trainwreck-style OT (30-watts, 6.6k primary) and a Fender blackface deluxe style PT (330-0-330, 5V/3A, and 6.3V/3A). I'll plan on using a GZ34 to get the B+ to around 430V. I'd like to use two EL34's as output tubes.

Questions:

1) Would 50/50/22/16/10/10 work for filtering as opposed to the 47/20/20/20/10/10 specified? That way I could use a 50/50 cap can for the OT and EL34s and some left over electrolytics for the rest.

2) What cathode resistor would you use for the EL34s? With approximately 390V on the plates and a 6.6k loading, I am ballparking 270R?

Thanks!

Title: Re: Tweed Overdrive Special Build
Post by: PRR on September 20, 2016, 06:07:46 pm

> 390V on the plates and a 6.6k loading, I am ballparking 270R?

I was right happy with 250r; but 2K of 3K common screen resistor.

At 400V and 6.6K load, it sits right at the top of class A but sags a bit when overdriven, and my scratchings suggested it would be very hard to kill with user abuse. (They had burned the PT once already, and I didn't want steady re-re-repair work.)

Title: Re: Tweed Overdrive Special Build
Post by: tubenit on September 20, 2016, 06:47:45 pm

You could use a 5V4 rectifier tube for more like 400v?  Then you'd use a 20uf - 32uf for the first filter cap and 50uf for the 2nd one and so on.

With respect, Tubenit