reverb driver transformer primary impedance question.

[katopan]

That's the right way to think about it technically. But finding a suitable 230k plate to plate transformer might be a challenge. Reverb doesn't need any real bass response, but also at that very high primary impedance the roll off might be starting as high as your upper mids. Transformer saturation would occur very easily anywhere below that and you might not be happy with the sound. A lower plate to plate impedance would give you back the typical frequency response for a reverb transformer and would probably still drive perfectly fine because triodes are very forgiving of their load (as has already been said). Just more to think about....

[martin manning]

That's the right way to think about it technically. But finding a suitable 230k plate to plate transformer might be a challenge. Reverb doesn't need any real bass response, but also at that very high primary impedance the roll off might be starting as high as your upper mids. Transformer saturation would occur very easily anywhere below that and you might not be happy with the sound. A lower plate to plate impedance would give you back the typical frequency response for a reverb transformer and would probably still drive perfectly fine because triodes are very forgiving of their load (as has already been said). Just more to think about....

Katopan, I'm not sure I follow you here. This is a hypothetical question I think, so the core size is unknown, but higher impedance would mean lower current and less chance of saturation, no?

[katopan]

The core is going to be as big as a PT to get the inductance high enough where the bass roll off isn't in the upper mids for that high a primary load impedance.

[martin manning]

Wouldn't it be ra//Zpri and Lpri? Can you cite a reference that explains?

[renshen1957]

The core is going to be as big as a PT to get the inductance high enough where the bass roll off isn't in the upper mids for that high a primary load impedance.

Hi,

Londonpower's Kevin O'Connor has advocated PP 12AT7 (the old self split design that dates from telegraphy days) since the 1990's and a variation of the circuit used a A Hammond 316 in a book he published 2004 with a layout. A Hammond 125A will work just as well to match the primaries of 23k to 8 ohm. With such smalls signals and a -40 dB drop after leaving the tank (transformer stepdown and mechanical losses) the output after the recovery amp is going to be guitar level, insufficient to drive a speaker.

Best Regards,

Steve

[katopan]

Sorry Martin, I feel my responses haven't been terribly clear. You can blame my 2 yo son who has been the cause of some sleep deprivation lately.

You're right about ra//Zpri. I was defaulting to pentodes where ra is very large. My train of thought was with a primary load of 230k and the typical reverb transformer low inductance Lpri, the bass rolloff freq is going to be very high (even for reverb duties). I know this is hypothetical but I was also jumping ahead knowing how many 230k:8ohm reverb transformers are readily available (none). The theory of doubling the original impedance for what each side of the standard 12AT7 reverb driver 'sees' and then x4 for push pull is good but it doesn't need to be that hard, and I think the standard transformers that are readily available would still work fine.

Steve - I appreciate that, but you mention 23k primary load where the original poster was talking 230k.