I have acquired a pair of Thordarson T-45901 1:4 interstage transformers which were designed for 6C5 PP tubes. I cant find a schematic for this tube. Are there any other schematics that I could use with this interstage? I would like to use them in a linestage. The transformers measure 750R : 12K
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An inter-stage transformer is not a line out transformer, although you could use it in this manner it would most likely be ill advised. The impedance ratio looks to me like it is more suitable for driving output tubes from a triode driver tube.
I would recommend spending some time google'ing and trying to find a catalog with more information.
Otherwise, search this forum for information on how to test a transformer and characterize it to see what it might be useful for.
I would recommend spending some time google'ing and trying to find a catalog with more information.
Otherwise, search this forum for information on how to test a transformer and characterize it to see what it might be useful for.
Gungnir: That transformer (1:4) appears to be a step up transformer. Impedance ratio goes as square of turns ratio. Probably for 10 k primary (CT) to 160 k (CT) PP grids. Try the Thordarson and the part number in Google. Someone has to have a Thordarson catalog on line.
If you want to match a tube to line, the high number goes first. For example, matching a 417A (2500 ohm plate load) to a 500 ohm line requires a 2:24:1 transformer.
Without knowing more about the characteristics of that particular transformer, you MAY (not guaranteed) use the secondary as the primary, and the primary as the secondary. The transformer is a impedance matching device. In this instance, the 4:1 turns ratio represents a 16:1 impedance ratio. Therefore, a 5 k plate load will transform to a 312 ohm "output" load. However, the frequency response and other characteristics may not be optimal. The insulation voltage should be looked up. The core of the transformer is probably not gapped, so always run a PP transformer in push pull to avoid core saturation.
If you want to match a tube to line, the high number goes first. For example, matching a 417A (2500 ohm plate load) to a 500 ohm line requires a 2:24:1 transformer.
Without knowing more about the characteristics of that particular transformer, you MAY (not guaranteed) use the secondary as the primary, and the primary as the secondary. The transformer is a impedance matching device. In this instance, the 4:1 turns ratio represents a 16:1 impedance ratio. Therefore, a 5 k plate load will transform to a 312 ohm "output" load. However, the frequency response and other characteristics may not be optimal. The insulation voltage should be looked up. The core of the transformer is probably not gapped, so always run a PP transformer in push pull to avoid core saturation.
> a 5 k plate load will transform to a 312 ohm "output" load.
Except the nominal 120K-160K secondary surely has at least 8K of winding resistance. A 312r load is a bad fit. Even a 10K modern input is not a great fit. Worse because there may be significant stray inductance which will roll-off on a lower-Z load than a couple naked negative grids.
> downloaded the Thordarson catalog
Thordarson was in business many-many decades. While many of their transformers stayed the same, I think there was at least one re-numbering of part designations. And true, this could have been a "custom", though there's a lot on eBay for it to be a one-off.
This kit-sales brochure shows push-pull 6C5 drivers and interstage irons with numbers like T-9005, T-5870, and T-7432 (not a T45901). (note prices: $4 and $12!!)
Amplifier plans from 1934. No 6C5 yet, but some of these plans could be adapted for true 1934 sonics. (type '46 triode-strapped?)
A full 1944 catalog.
It looks like between 1937 and 1944 they added a letter in the middle of the number. Your part may be very old.
Note that in Thordarson lingo, you have an "interstage". Nominally zero power at high impedance, step-up. A step-down, as to drive class 2 grids, is a "driver".
> a 6C5 into a PP 6B4G? too much gain?
Push-Pull 6C5; and yes that's still a stupid bunch of gain. The little triodes will swing at least 50V maybe 100V at the plates. That's 200V-400V at the grids of the big triodes!! Even 2A3/etc don't need near that much. 1:2 maybe 1:3 is all we ever used.
I can't imagine why they made this.
Except the nominal 120K-160K secondary surely has at least 8K of winding resistance. A 312r load is a bad fit. Even a 10K modern input is not a great fit. Worse because there may be significant stray inductance which will roll-off on a lower-Z load than a couple naked negative grids.
> downloaded the Thordarson catalog
Thordarson was in business many-many decades. While many of their transformers stayed the same, I think there was at least one re-numbering of part designations. And true, this could have been a "custom", though there's a lot on eBay for it to be a one-off.
This kit-sales brochure shows push-pull 6C5 drivers and interstage irons with numbers like T-9005, T-5870, and T-7432 (not a T45901). (note prices: $4 and $12!!)
Amplifier plans from 1934. No 6C5 yet, but some of these plans could be adapted for true 1934 sonics. (type '46 triode-strapped?)
A full 1944 catalog.
It looks like between 1937 and 1944 they added a letter in the middle of the number. Your part may be very old.
Note that in Thordarson lingo, you have an "interstage". Nominally zero power at high impedance, step-up. A step-down, as to drive class 2 grids, is a "driver".
> a 6C5 into a PP 6B4G? too much gain?
Push-Pull 6C5; and yes that's still a stupid bunch of gain. The little triodes will swing at least 50V maybe 100V at the plates. That's 200V-400V at the grids of the big triodes!! Even 2A3/etc don't need near that much. 1:2 maybe 1:3 is all we ever used.
I can't imagine why they made this.
> I can't imagine why they made this.
Going to bed, I imagined a use.
Classic AM radio transmitters had a BIG audio amplifier. 10KW of carrier needs 5KW of audio. NFB is problematic. Pentodes this size were not done. Tetrodes kink. Class B is most efficient but notchy. Mostly they used LOW-Mu triodes to get transformer damping and smooth AB1 sound.
If we postulate 1,000V-1,500V supply to this 5KW amp, and Mu like 5, we do need "200V-400V at the grids of the big triodes". A pair of 6C5 will drive this. The 6C5 grids can be driven from a +10dBm studio line with a 1:10 line-to-PP-grids transformer. The whole audio section from 10mW to 5,000 Watts was sometimes this simple. And 6C5 would be one of the few types stocked by every radio station.
Going to bed, I imagined a use.
Classic AM radio transmitters had a BIG audio amplifier. 10KW of carrier needs 5KW of audio. NFB is problematic. Pentodes this size were not done. Tetrodes kink. Class B is most efficient but notchy. Mostly they used LOW-Mu triodes to get transformer damping and smooth AB1 sound.
If we postulate 1,000V-1,500V supply to this 5KW amp, and Mu like 5, we do need "200V-400V at the grids of the big triodes". A pair of 6C5 will drive this. The 6C5 grids can be driven from a +10dBm studio line with a 1:10 line-to-PP-grids transformer. The whole audio section from 10mW to 5,000 Watts was sometimes this simple. And 6C5 would be one of the few types stocked by every radio station.
> 200V-400V at the grids of the big triodes!!
This does lead to day-dreams of a Cathode Follower Output Stage power amp. Imagine a pair of 2A3 (or 6B4), cathode-loaded. We will need like 220V of grid swing at each side. It *appears* your transformer can do this.
Well, OK, 2A3/6B4, this would be a "filament follower". Which points out that the filaments can not be connected to the same filament supply, you nee two windings of good voltage breakdown. Even with heater-cathode tubes, the cathodes will be swinging hundreds of volts apart, more than most heater insulation can stand, so you still need separate heater windings. While a few pass-tubes have high insulation ratings they are often specced only for positive voltages. Hmmm, 6080 does allow 300V either way, so you might get away with a common heater supply.
Of course this is no "line stage", and requires multiple not-cheap additional transformers just so you can use the transformer(s) in your hand.
This does lead to day-dreams of a Cathode Follower Output Stage power amp. Imagine a pair of 2A3 (or 6B4), cathode-loaded. We will need like 220V of grid swing at each side. It *appears* your transformer can do this.
Well, OK, 2A3/6B4, this would be a "filament follower". Which points out that the filaments can not be connected to the same filament supply, you nee two windings of good voltage breakdown. Even with heater-cathode tubes, the cathodes will be swinging hundreds of volts apart, more than most heater insulation can stand, so you still need separate heater windings. While a few pass-tubes have high insulation ratings they are often specced only for positive voltages. Hmmm, 6080 does allow 300V either way, so you might get away with a common heater supply.
Of course this is no "line stage", and requires multiple not-cheap additional transformers just so you can use the transformer(s) in your hand.
PRR: The Gates BC5E AM transmitters used a 3CX2500F3 Eimac triode as the 5 kw RF final, and the modulator was a pair of push pull 3CX2500 F3 triodes. These were driven by 845's in push pull parallel. There was a large negative feedback ladder with resistors and caps across them since a single resistor couldn't take the 5 kV plate voltage (at 100% positive peak modulation this went to 10 kV peak). I recall the 845's were driven by PP 807's...and the stages were transformer coupled. The RCA 5 and 10 kw transmitters used 5762 triodes. The plate voltage was also around 5 kilovolts..the 5 kw RCA BTA5H used one 5762 as RF final, and the BTA10H used two 5762's in parallel...the anode current on the 5 kW version ran around 1.3 amps, and the 10 kw version ran around 2.8 amps anode current, with 5 kV anode voltage on each...At any rate, the modulator had to furnish at least 50% power to modulate the RF final to 100%. (If asymmetrical positive peak audio for loudness was desired, the modulator had to furnish additional audio power to carry the positive peak..the FCC permits 125% positive peak modulation for AM broadcast...) The problem with the 3CX2500F3 as a 5 kW RF final was the peak cathode emission at 100% emission was insufficient....and tube life wasn't that good...
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