I'm looking to use my Bogen PA chassis that was setup for (I think) 30 watts from a pair of 7868 tubes. The original PT was a cheap piece of tinfoil so I was planning to use the monster PT from a Hammond A0-35 reverb amp. I thought that it would work well with either 2 or 4 el84's. The original OT is a beefy paper wound affair, its bigger than the PT with a primary of 5.8k and 4, 8 and 16 ohm taps. I have a set of turret boards from Watts and was going to try it. It's probably not the best use of the old iron. I think I have over $120 invested in the two old amps. I just don't think much of the Hammond OT or the Bogen PT.
Anyone think it would be a good idea ?
Viability of a Liverpool build Hammond A0-35 + Bogen CH-35
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: Viability of a Liverpool build Hammond A0-35 + Bogen CH-35
4xEL84s will fool you in terms of current demand. We use transformers rated at 200ma in that application, some of them run hot. It depends on how optimistic the ratings are. Trainwrecks use beefy transformers, that's part of the tone.
In general if the amp ran 2xEL84s to begin with it's asking a lot for it to run 4xEL84s.
When the last AO-35 goes the way of the dinosaurs and gets converted to a guitar amp we'll all lament about the good ol' days when we could still get them.
The Bogen ran 7868s to begin with. It will easily run 2x6V6 with the stock PT, no cuttin', fittin', or screwin' around required. Just yank the 7868 sockets and drop in a set of octals. I used to butcher Ampegs with that mod all the time.
Or... talk to the guy a couple threads over who doesn't like his Vintage 30 (4xEL84s). Maybe you two can work something out.
In general if the amp ran 2xEL84s to begin with it's asking a lot for it to run 4xEL84s.
When the last AO-35 goes the way of the dinosaurs and gets converted to a guitar amp we'll all lament about the good ol' days when we could still get them.
The Bogen ran 7868s to begin with. It will easily run 2x6V6 with the stock PT, no cuttin', fittin', or screwin' around required. Just yank the 7868 sockets and drop in a set of octals. I used to butcher Ampegs with that mod all the time.
Or... talk to the guy a couple threads over who doesn't like his Vintage 30 (4xEL84s). Maybe you two can work something out.
Re: Viability of a Liverpool build Hammond A0-35 + Bogen CH-35
The Bogen CH-35 chassis is now gutted. I saved what I could but they were not a the best built amps of the period. I think the PT's were wired with a CT winding to a non CT winding in series or some reasonably bizarre turn. Under filtered too -way.
My fault for not researching the amp before I bought it on eBay. I thought the chassis was clean and nice but the steel was just flimsy. If I can sell the 7868 tubes and sockets I might not be completely hosed.
My impression of the AO-35 PT was that it (or a similar sized unit) also ran a a daughter chassis in other organs and I believe it's used in a Hammond PR20 tone cabinet that used 3 sets of 6v6 and/or el84 output tubes. Plus its a lot bigger than the 15 watt TDS PT I have which is well under rated for it's application. I hope my thinking holds water.
With the 7868 19 watts of plate dissipation and 550 max plate voltage would a pair be a better choice for a Stangray or Rocket than a high gain amp like the Liverpool. Might be worth a spin, ya think ?
My fault for not researching the amp before I bought it on eBay. I thought the chassis was clean and nice but the steel was just flimsy. If I can sell the 7868 tubes and sockets I might not be completely hosed.
My impression of the AO-35 PT was that it (or a similar sized unit) also ran a a daughter chassis in other organs and I believe it's used in a Hammond PR20 tone cabinet that used 3 sets of 6v6 and/or el84 output tubes. Plus its a lot bigger than the 15 watt TDS PT I have which is well under rated for it's application. I hope my thinking holds water.
With the 7868 19 watts of plate dissipation and 550 max plate voltage would a pair be a better choice for a Stangray or Rocket than a high gain amp like the Liverpool. Might be worth a spin, ya think ?
Re: Viability of a Liverpool build Hammond A0-35 + Bogen CH-35
I've done a number of these sort of PA conversions, although never anything as agressive as a Bogen -> Liverpool.
Please post a photo of yout chassis - maybe only cause I am interested, but you never know what other useful comments could arise.
Please post a photo of yout chassis - maybe only cause I am interested, but you never know what other useful comments could arise.
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: Viability of a Liverpool build Hammond A0-35 + Bogen CH-35
The PR-20 uses a different transformer. It's larger.chopstuck wrote:My impression of the AO-35 PT was that it (or a similar sized unit) also ran a a daughter chassis in other organs and I believe it's used in a Hammond PR20 tone cabinet that used 3 sets of 6v6 and/or el84 output tubes. Plus its a lot bigger than the 15 watt TDS PT I have which is well under rated for it's application. I hope my thinking holds water.
Oh... for the guy who wants two rectifiers in his Twin. Instant Dual Rectifier, eh?
Anyway... the early PR-40 cabinet has a massive power supply with 2x5U4G. The "E" model console amp is pretty cool too, it has a PT w/ dual HT and dual rectifier windings. One winding runs the main amp w/ 7591s, the other one runs the reverb amp w/ ECL86s.