new project

[dwhutchens]

I have an old power amp out of a phonograph. I want to use the transformers and build a new amp from scratch. The amp had 6k6 tubes in it. I slapped together a preamp and it doesn't sound to bad but the chassis is too cramped and I'd like to use 6v6 power tubes if possible. The number stamped on the output transformer is LH265061-1 and under that is 366848. Anybody know the primary impedance of that. If not I put 8vac across the secondary with an ac wall wart and measured 494vac across the primary if anybody knows the math. The amp had a 5y3 rectifier. I'm thinking maybe a 5e3, any other suggestions.
David

[Bruce / Mission Amps]

I have an old power amp out of a phonograph. I want to use the transformers and build a new amp from scratch. The amp had 6k6 tubes in it. I slapped together a preamp and it doesn't sound to bad but the chassis is too cramped and I'd like to use 6v6 power tubes if possible. The number stamped on the output transformer is LH265061-1 and under that is 366848. Anybody know the primary impedance of that. If not I put 8vac across the secondary with an ac wall wart and measured 494vac across the primary if anybody knows the math. The amp had a 5y3 rectifier. I'm thinking maybe a 5e3, any other suggestions.
David

If your voltages were correct... you need to measure the low voltage while under the load of the output tranny winding... you have 3K8:1 secondary.
That would mean with an 8 ohm speaker the secondary would be 30K5!!!
Even with a 4 ohm speaker load it would be +15K. That's probably OK for 6K6GTs but a bit too high for 6V6s.
It would be OK with a pair of 4 ohm loads in parallel though.
If you haven't, recheck the wall wart voltage while connected to the OT and see if it isn't lower.
Unfortunately that would make the OT secondary even worse.

[dwhutchens]

I did check the voltage on the wall wart while it was connected to the transformer. I unsoldered the secondary ground, disconnected the speaker and pulled the tubes but left the center tap grounded, I didn't think that would make a difference. I had the wall wart plugged into a variac and I set it to exactly 8vac. I was going to dial it up to 10 but it wouldn't go that far so I backed it off to 8. So are you saying I need a 2 ohm load for 6v6 tubes?

Also I just checked the power transformer. It appears to be 345-0-345 and has 5vac and 6.3vac taps. The numbers stamped on it are LH265050-1 and366832.

David

[Bruce / Mission Amps]

I did check the voltage on the wall wart while it was connected to the transformer. I unsoldered the secondary ground, disconnected the speaker and pulled the tubes but left the center tap grounded, I didn't think that would make a difference. I had the wall wart plugged into a variac and I set it to exactly 8vac. I was going to dial it up to 10 but it wouldn't go that far so I backed it off to 8. So are you saying I need a 2 ohm load for 6v6 tubes?

Also I just checked the power transformer. It appears to be 345-0-345 and has 5vac and 6.3vac taps. The numbers stamped on it are LH265050-1 and366832.

David

Well, you should not have your OT secondary center tap grounded.
Why? It isn't grounded in the amp anywhere... it is where the B+ from the power supply enters the OT.
From what I read in your other post, yes 2 ohms would be better then 4 ohms.

[dwhutchens]

Duh! I had power transformer on my mind when I wrote that If I keep the 6k6 tubes what kind of power should I expect and would the optimum speaker load be 4 or 8 ohms. Can you recommend a circuit useing the 6k6's. I guess maybe I could put four 8" 8ohm speakers in a cabinet and go for the 6v6's, that might be interesting. Sorry for all the questions and thanks much for the responce.
David

[Synaptic Amps]

Sounds like you've scored a sweet power transformer. If I were you I'd use solid state rectifiers to get every last volt possible off the secondary to the plate of your 6V6. The more juice you save off that 5V filament line the more you'll be able to really get that output tube cranking. You could run a pilot light off the 5V line to give it something to do - I honestly prefer how a typical 6V pilot bulb runs a little less bright off an unused 5V line. With the current you could save by elliminating the rectifier tube you might even be able to run a 6L6. You'll know how much you can get away with once you get your amp wired up and running. Just monitor the power transformer with your hands to see how hot it gets. You want it warm but not hot.

It seems to me as though the cost of obtaining 4 drivers would negate any potential savings gained by not buying suitable output iron in the first place. On the other hand, if salvaging is the name of the game, a pair of 4 ohm 8" or 10" drivers shouldn't be too difficult to come across. I wouldn't be surprised if the phonograph was running a pair of 4 ohm 8s in the first place.