UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - OK need assistance or clarification of output transformer values

joebog1 · 30th Mar 2020, 12:40 am

When you parallel two valves, be they triodes, tetrodes or pentodes the impedance will be divided by 2. So your first assumption is correct, it will become 3250 ohms Ra.
Your choice of Hammond 125B will work OK. . Current in the transformer will be HALF your 26 mA as there will be 13mA per side. The total flowing into the centre tap will be 26 mA, but that splits in half and 13 mA goes to each output valve.

Here is some reading for you, it is explained fairly well I believe.

http://www.r-type.org/articles/art-010d.htm

Joe

30th Mar 2020, 12:40 am	#2
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: OK need assistance or clarification of output transformer values When you parallel two valves, be they triodes, tetrodes or pentodes the impedance will be divided by 2. So your first assumption is correct, it will become 3250 ohms Ra. Your choice of Hammond 125B will work OK. . Current in the transformer will be HALF your 26 mA as there will be 13mA per side. The total flowing into the centre tap will be 26 mA, but that splits in half and 13 mA goes to each output valve. Here is some reading for you, it is explained fairly well I believe. http://www.r-type.org/articles/art-010d.htm Joe