Starting my first classic amp restoration and have an output transformer question.The Harmony H205 amp I bought, had the OT replaced with a 16 ohm output sub. It’s a 6V6 pp circuit, rated at 12W I believe?. Haven’t gotten to the point of powering it up yet, but will obviously need a better OT. That orange cap needs to go too
This amp has the original Rola 12”, 3.2 ohm speaker. Any suggestions on a quality OT would be greatly appreciated. Want to do justice to this classic.
This amp has the original Rola 12”, 3.2 ohm speaker. Any suggestions on a quality OT would be greatly appreciated. Want to do justice to this classic.
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Now you’ve got me thinking, do have some transformers I could rewind.
Let me post the schematic.
Cool amp... I would appreciate very much if you posted a sound clip somewhere after its all patched up! Hope you get it up and running in short time and make it look cooler... I think that any 6V6 PP OT would get along inside it... If you can, buy something used and vintage, or make your own if its not a problem.
Working on calculating plate current but the schematic I found is hard to read. I calculated 12w dissipation per tube which seems really high. Plate voltage is 310v with a 200ohm, 5W cathode resistor. Sure about the 310v and 200ohm.
The mounting holes in the chassis are 2-13/16” Pretty crusty inside the chassis I have to say.
I will definitely post audio, one of my son’s friends can supply the guitar input. I play a little harp so I might throw some in as well. The current plan is to sell it when I’m done.
The OT in it now is a Merit A 2936. I found a catalog that lists it as a universal type “PP 6V6 Class AB1, 75 mA Pri. D.C. 18W” The main reason I want to replace it is the hole spacing is too small so someone mounted it with one screw and but twine around it to hold the shell! Otherwise it may not be that bad of a sub.
The mounting holes in the chassis are 2-13/16” Pretty crusty inside the chassis I have to say.
I will definitely post audio, one of my son’s friends can supply the guitar input. I play a little harp so I might throw some in as well. The current plan is to sell it when I’m done.
The OT in it now is a Merit A 2936. I found a catalog that lists it as a universal type “PP 6V6 Class AB1, 75 mA Pri. D.C. 18W” The main reason I want to replace it is the hole spacing is too small so someone mounted it with one screw and but twine around it to hold the shell! Otherwise it may not be that bad of a sub.
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That's what it should be. It is a self-bias amp. At idle it sucks all the power it could ever need and dissipates it as heat. (On signal, some of that power is diverted to speaker.)
To get the most out of the tube budget, the Designer will work the expensive tubes as HOT as is allowable. (Especially when sold on a short warranty.)
6V6 is *rated* for 12 Watts Pdiss. That's a target for when you do not measure every radio (amplifier) made. If your production is tested, 14W is allowed. And we know a recent Fender which put *17* Watts into a "6V6".
Attached is part of the old 6V6 datasheet, including one condition not found on most US sheets. None of these numbers are critical. Later Designers deviated very far from Suggestion and even Ratings, and pleased guitarists. But the older basic 2*6V6 amps hewed pretty close to how they would be used in a high-class radio (and using radio-market parts). Guitar amps tend to be run a bit hotter since the PT does not have to power a radio tuner, and guitarists can change their own tubes, and nobody expected this guitar-fad to last.
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It has a beefy power transformer. It almost looks like it has the orig, rubber insulated power cord and plug. The only parts that have been replaced are one of the filter cap cans, and the output transformer I believe. Grille cloth appears to have been replaced too.
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Well, one pot replacement from having this wrapped up! I’ll post many! pics I took along the way. Also want to post the schematic of the unusual instrument input circuit.
Not sure anyone reading this forum will be repairing one of these any time soon, but you never know?
I learned that if you need to restore a rusted chassis, better be ready to roll up your sleeves!!
Not sure anyone reading this forum will be repairing one of these any time soon, but you never know?
I learned that if you need to restore a rusted chassis, better be ready to roll up your sleeves!!