Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: duke of earl on February 01, 2012, 08:28:44 pm

Title: OT for AB763
Post by: duke of earl on February 01, 2012, 08:28:44 pm

a few years ago I built my first amp-A Hoffman AB763 circuit for 2x6L6 tubes. I used a 100 watt PT and a 100 Watt OT for more headroom. I also used a GZ-34 Port Arthur Rectifier (Gerald Weber Mod) to get a little compression on the front of the note which works very nicely. I am toying with the idea of going with a 50 watt OT as I want the amp to breakup moderately but still maintain descent clean headroom. I have actually put some EH 6v6"s in the amp and put a 15k feedback resistor in and I'm not really digging the overdriven tone with this setup. The speakers are 1 Weber Legacy 12"and 1 Weber California Alnico 12". The speakers are not broke in yet and I wonder should I wait for the speakers to settle in before making any changes to the topology? Your thoughts are much appreciated.

Title: Re: OT for AB763
Post by: duke of earl on February 02, 2012, 04:32:35 pm

speakers are 16 ohm each run in parallel. The circuit is a Hoffman Board layout for the most part with some tweaks.

Title: Re: OT for AB763
Post by: duke of earl on February 02, 2012, 07:29:33 pm

If you look in Doug's circuits, you will see an AB 763 that he tweaked. It is found under the Hoffman Board Building Section in the Library.

Title: Re: OT for AB763
Post by: EL34 on February 03, 2012, 06:36:19 am

018343
It's a great OT. I sell alot of them and people really like them.
http://www.hoffmanamps.com/MyStore/catalog/parts1.htm (http://www.hoffmanamps.com/MyStore/catalog/parts1.htm)

I have one in my Super Vibrolux Reverb with a pair of EH 6V6's but I have also used it with 6L6's

Title: Re: OT for AB763
Post by: duke of earl on February 05, 2012, 08:50:06 pm

Thanks Doug. How do the 6v6's respond to this model?

Title: Re: OT for AB763
Post by: Dave on February 05, 2012, 09:38:04 pm

You said you were using a 100 watt PT. So, you intend to use a pair of 6V6's with a Twin Reverb PT and a Super Reverb OT?
First, are you looking to find out how quickly you can kill a pair of 6V6's?
Second, you will create a 100 percent mismatch between your OT and your speakers by using 6V6's.
It will work, but it seems pretty, hmm, unorthodox.
Ever see a Volkswagon Beetle with a V12 and a power glide transmission?

Dave

Title: Re: OT for AB763
Post by: duke of earl on February 06, 2012, 08:55:14 pm

Dave,

I originally used 6l6's and by using the bigger OT, doubled the speaker impedance to match the reflected impedance. Doug says the Electro Harmonix 6v6's can handle the plate volts in a Twin Reverb so I thought I'd give em a try. I'm still a novice to amp building and am trying different things to feel out what works and what doesn't. When I had the 6l6's in the amp, I blew my California speakers so I wanted lower wattage output tubes after the recone job. You could say I am adventuress in my endeavor! Thanks for your advice and to all who are posting here.
Weber speakers (http://www.youtube.com/watch?v=LNXjpblvOwQ#)
Getting the Eric Johnson Tone (http://www.youtube.com/watch?v=E909LqLTbYg#)

Title: Re: OT for AB763
Post by: Willabe on February 06, 2012, 09:46:42 pm

Yes tell me, Why does love have to be so sad?

You sound good Duke.


                  Brad    :icon_biggrin:

Title: Re: OT for AB763
Post by: PRR on February 06, 2012, 11:57:35 pm

> When I had the 6l6's in the amp, I blew my California speakers

The Weber California? That's suggested to be "like a JBL" and really should eat ALL the output of a couple 6L6. I wonder what went wrong?

Title: Re: OT for AB763
Post by: duke of earl on February 07, 2012, 02:51:30 pm

I played the amp on "11" with overdrive and humbuckers for a couple of years. Yes they are weber alnicos @ 65 watts a piece.