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Old 28th October 2009, 03:32 AM   #1
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Default Vintage output transformers

Anyone here use vintage output transformers to build their single ended DHT triode amp?

I've mostly seen 45, 2A3, 300B amps with modern transformers like James, Electraprint, Tango, Hammond, etc... but never with vintage output transformers that came from those little RCA, Zenith single ended amp that use 6BQ5s, 6V6, etc.... Are these old OPT not up to the task "sound quality wise".
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Old 28th October 2009, 03:56 AM   #2
TheGimp is offline TheGimp  United States
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A lot of those old transformers were wound with the primary first and secondary on top with no interleave. Look at the layers to see if you can identify which is which.

If they are would like I described, they will be low quality.

High quality audio transformers will have alternate layers of primary and secondary windings to minimize capacitive coupling and leakage inductance.

The latter is critical in high bandwidth linear transformers.

Mass is good also. primary Inductance is a function of the cross section of the core, which is directly related to mass.
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Old 28th October 2009, 10:24 AM   #3
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Quote:
Originally Posted by TheGimp View Post
High quality audio transformers will have alternate layers of primary and secondary windings to minimize capacitive coupling and leakage inductance.

The latter is critical in high bandwidth linear transformers.

Mass is good also. primary Inductance is a function of the cross section of the core, which is directly related to mass.
hey-Hey!!!,
Capacitance goes up with more interleaves, but leakage L goes down. got to make the trade carefully. Primary L is also a f'n of primary turns, more means more capacitance but lower AC flux density( and higher DC flux density ), so again with the trades...
cheers,
Douglas
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Old 28th October 2009, 04:53 PM   #4
kevinkr is offline kevinkr  United States
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Low to moderate rp triodes are more tolerant of stray capacitance, and less tolerant of leakage inductance because the series leakage reactance may be a appreciable % of rp at higher frequencies - this can have a drastic effect on high frequency performance. So here the trade off should be less leakage inductance at some expense in increased stray capacitance.

Note that some of the bigger power triodes have relatively high rp and in such cases the trade offs should be in the direction of favoring low stray capacitance over leakage inductance. (Types like the 211 and 845)

Pentodes and UL connection typically have high to moderate rp and here leakage inductance is better tolerated because the leakage reactance is a smaller % of rp than is typically the case with triodes or triode connection. In this case trade off leakage inductance for lower stray capacitance which shunts rp and causes HF roll-off.

The optimizations for different applications are necessarily different, some designer/builders are able to make pretty good compromises that work well for both.

There were undoubtedly good SE transformers back in the day, but you won't find them in consoles. Western Electric comes immediately to mind, possibly Thordarson, UTC and others might have usable devices.. Until you asked it never occured to me to even check. Obviously back in the late 1930s and perhaps even later people had to be making something, but the trend from the early 1930s onwards was towards pushpull. (I have a 1932 Atwater Kent 310 chassis in working order and it has an IT driven PP output stage.)

Anything good has probably long since ended up in the Orient where such items were appreciated when we were still largely dumping the stuff into landfills as obsolete.
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Old 29th October 2009, 05:14 AM   #5
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Thank you for giving me your insight about the old OPT from the console. I guess I won't bother with them. Thanks again.
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