Starting to think about next year's project.
I have been interested in the RCA 96A and 86A series as they are feedforward designs like the Group DIY 26C, which I hope will go up for auction soon.
I plan to make a simple pre-war design like a modified 96A. The final iteration of the old 6 pin 89 tube used in that was the octal 6K6GT, which is a low output tube, more in keeping with studio use.
The side-chain presents problems as the transformer is no longer available and in any case it is only fed by one of the signal phases. The interstage is not really necessary nowadays either, but it was typical of pre-war designs; the price of copper must have been dirt cheap back then, as was labour. I discovered with the 26C that the top end compression is very important so it is essential that the compressor has a full range up to 20kHz, this is much easier/cheaper with tubes than transformers.
I am guessing that the 86A was a later version of the 96A with uprated tubes, the component values remaining much the same. Well I'll have to assume that they were as there are none shown on the 96A schematic.
I have designed an all tube side-chain to take the place of the transformer, an extra tube is a fraction of the cost of a transformer, I am guessing this was not the case before the war.
Anyway, I shall give it a go, I will probably sell it when its finished, I plan to make vintage P2P tube designs for sale in my retirement in two years time, got to keep the brain active!
best
DaveP
I have been interested in the RCA 96A and 86A series as they are feedforward designs like the Group DIY 26C, which I hope will go up for auction soon.
I plan to make a simple pre-war design like a modified 96A. The final iteration of the old 6 pin 89 tube used in that was the octal 6K6GT, which is a low output tube, more in keeping with studio use.
The side-chain presents problems as the transformer is no longer available and in any case it is only fed by one of the signal phases. The interstage is not really necessary nowadays either, but it was typical of pre-war designs; the price of copper must have been dirt cheap back then, as was labour. I discovered with the 26C that the top end compression is very important so it is essential that the compressor has a full range up to 20kHz, this is much easier/cheaper with tubes than transformers.
I am guessing that the 86A was a later version of the 96A with uprated tubes, the component values remaining much the same. Well I'll have to assume that they were as there are none shown on the 96A schematic.
I have designed an all tube side-chain to take the place of the transformer, an extra tube is a fraction of the cost of a transformer, I am guessing this was not the case before the war.
Anyway, I shall give it a go, I will probably sell it when its finished, I plan to make vintage P2P tube designs for sale in my retirement in two years time, got to keep the brain active!
best
DaveP