Hey guys,
I have a fairly hefty output transformer pulled from a Hammond that I want to do something with. I used a signal generator to measure the turns ratio and figure out the primary impedances at different frequencies.
At frequencies from 100 to 1K, the primary impedance would be 2.7k into 4 ohms and 5.4k into 8 ohms.
At 2.5k in, primaries are 2.2k and 4.5k into 4 and 8 ohms.
At 5k in, the primaries would be 1.5k and 3k into 4 and 8 ohms.
This transformer was originally powered by a pair of 7591's, but I have a pile of 6l6's that I'd like to use some of. That said, I'm up for just about anything that would suit the primary impedances. Any suggestions?
Soliciting opinions on use for a particular OT
Moderators: pompeiisneaks, Colossal
Re: Soliciting opinions on use for a particular OT
is it a Single ended or Push-Pull OT ?
depending on that would also be how much power the OT can handle.
7591 have a maximum plate dissipation of 19 Watts i think.
a primary Impedance of ~4K could work well with 6L6 in Class A or if it is SE (parallel) you could run it asymmetrically, which i hear soudns great in higher gain designs.
what are you looking for anyway? hifi ? guitar? (clean'ish or high gain'ish ?)
depending on that would also be how much power the OT can handle.
7591 have a maximum plate dissipation of 19 Watts i think.
a primary Impedance of ~4K could work well with 6L6 in Class A or if it is SE (parallel) you could run it asymmetrically, which i hear soudns great in higher gain designs.
what are you looking for anyway? hifi ? guitar? (clean'ish or high gain'ish ?)
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gingertube
- Posts: 531
- Joined: Mon Nov 14, 2011 2:29 am
- Location: Adelaide, South Oz
Re: Soliciting opinions on use for a particular OT
Matt D,
I'm not sure that you measured these correctly.
You should measure the turns ratio at a single frequency anywhere between 500Hz and 1KHz. Most folk arbitrarily choose something - I use 600Hz, its not that critical.
When you measure the turns ratio (= to the voltage ratio) you MUST do that unloaded. That is if you drive the secondary and measure the primary then do not load that primary. Similarly if you drive the primary and measure the secondary it should not be loaded.
You mentioned that it was previously driven by a pair of 7591. Take a look at the 7591 datasheet and application data and it will show that the tranny is almost certainly a 6600 Ohms Raa Primary and based upon your initial measurement an 8 Ohm secondary. Power Rating is probably 45 Watts (thats what a pair of 7591 will deliver with a 6600 Ohms Raa Output Tranny).
A pair of 6L6 in Class AB1 at around 450V rail will deliver about 50 Watts into 6600 Ohms Raa. Thats a good match.
So go for it - best wishes,
Ian
I'm not sure that you measured these correctly.
You should measure the turns ratio at a single frequency anywhere between 500Hz and 1KHz. Most folk arbitrarily choose something - I use 600Hz, its not that critical.
When you measure the turns ratio (= to the voltage ratio) you MUST do that unloaded. That is if you drive the secondary and measure the primary then do not load that primary. Similarly if you drive the primary and measure the secondary it should not be loaded.
You mentioned that it was previously driven by a pair of 7591. Take a look at the 7591 datasheet and application data and it will show that the tranny is almost certainly a 6600 Ohms Raa Primary and based upon your initial measurement an 8 Ohm secondary. Power Rating is probably 45 Watts (thats what a pair of 7591 will deliver with a 6600 Ohms Raa Output Tranny).
A pair of 6L6 in Class AB1 at around 450V rail will deliver about 50 Watts into 6600 Ohms Raa. Thats a good match.
So go for it - best wishes,
Ian
Re: Soliciting opinions on use for a particular OT
Thanks for the replies. I'll try it again. With my signal generator set at 1 Volt and 600 Hertz I attached the the leads from the signal generator to the leads from the transformer that attached to the plates of the tubes (the primary right?). Then I measured 26 Volts AC on the output (secondary?) side of the transformer. 26v squared is 676. 676 x 4(ohms)= 2704. 676 x 8 (ohms) = 5400.
So that would be a 5.4k primary impedance. Am I doing that correctly?
So that would be a 5.4k primary impedance. Am I doing that correctly?
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gingertube
- Posts: 531
- Joined: Mon Nov 14, 2011 2:29 am
- Location: Adelaide, South Oz
Re: Soliciting opinions on use for a particular OT
Matt,
26V on the primary (anode connections) to 1 V on the secondary I could believe
OR 1 V on the secondary and 26V on the primary.
BUT
26V on the secondary for 1 v on the primary is just wrong.
Assuming that you just got the readings reversed in what you typed 5.4K is correct and that would be fine for a pair of 6L6.
Cheers,
Ian
26V on the primary (anode connections) to 1 V on the secondary I could believe
OR 1 V on the secondary and 26V on the primary.
BUT
26V on the secondary for 1 v on the primary is just wrong.
Assuming that you just got the readings reversed in what you typed 5.4K is correct and that would be fine for a pair of 6L6.
Cheers,
Ian