Recently, I got a mess of transformers and such parted from an old Baldwin organ. Included were two massive power transformers (they probably ran whole banks of tubes for the tone generators and dividers), a 7H choke, a bathtub oil cap, one (aw, shucks) output transformer that looks to be 6k with a 16 ohm output, and one autotransformer. I understand the rest of the catch more or less, but can anyone who is conversant with the old Baldwin organs fill me in about the purpose of the autotransformer. It's ungapped, and the primary inductance is very high. It occurs to me that it may be the timing element to a blocking oscillator, but again, maybe not. Does ayone have a clue about it?
That looks to work if you have a 50% tap on the transformer - unfortunately, mine was 17.5V out for 50V in, driven at 300Hz with a sine wave source I have on my bench at work. I use that source so I can get realistic readings for turns ratio and inductance by driving the transformer with a low impedance signal within its bandwidth. Since I have a sensitive Volt/Amp/Wattmeter hooked in series (a Yokogawa WT210) I can also derive primary inductance at a realistic excitation level.
The autotransformer idea as shown is a nice one for a rainy day.
The autotransformer idea as shown is a nice one for a rainy day.
What impedences is the autotransformer in schematic
Tubelab --
I have admired this schematic before -- I have a bunch of 6Bx7s. However, I am just too dumb to figure out what impedences the interstage needs be for this application. What is your guess as to the specs for the PSA-2N in this schematic. thx.
Tubelab --
I have admired this schematic before -- I have a bunch of 6Bx7s. However, I am just too dumb to figure out what impedences the interstage needs be for this application. What is your guess as to the specs for the PSA-2N in this schematic. thx.
Yes the "interstage transformer" has a single center tapped winding that can effectively be used as a phase splitter without a secondary. The "impedance" isn't a factor here, but the transformer that is used must have enough inductance to work at low frequencies, and it should have a low enough winding capacitance to avoid phase shifts at the high frequencies.
I have seen schematics like this dating back to the 1930's when transformers were cheaper than tubes and Hi Fi meant that you could play the AM radio or some 78 RPM vinyl. I would use a vacuum tube phase splitter today (I am partial to the LTP) but Jack is in business to sell transformers. People have built this amplifier using power toroids for the interstage and the OPT. You could use a "real" interstage transformer too.
Look through this thread for several variations on the same idea:
http://www.diyaudio.com/forums/tubes-valves/76820-idea-2-tube-6080-pp-amp.html?highlight=6as7
I was thinking of power toroids myself- I have a likely pair with 155-0-115 primaries sitting right by my elbow as I write this. I'd want to check out the inductance before I tried it. The Baldwin autoformer has a really high inductance. I'm going to look at it again, but even if it checks out as an even split, I only have one of them...
Do you have a model number for the Baldwin? Reason I'm asking is that there is one on an online auction here and the owner knows squat about it (neither do I) and its too far away for me to go and look to see if it's tube or not. Could be a good score if it is
Merry Xmas everyone,
Gary
I just recently parted out the amplifier from a Baldwin organ. The organ was bought new in 1962 by a church. The amp was removed from the organ and used for the church PA amp when the organ died a few years ago. The amp was given to me after it was replaced by a SS amp last year.
There is no numbers on the amp itself. The amp appears to have been totally seperated from the organ functions and did not furnish power to the organ. The clue here would be a rather large set of wires from the power transformer to supply filament power to the tone generator tubes.
It had a rather large power transformer, used 8 X 6BQ5 (EL84) tubes, 2 X 5U4 tubes, and 3 X 12AX7 tubes. There were 3 audio channels. The main channel used 4 X 6BQ5's and produced about 30 watts. The output transformer was about 5 pounds which would have been sufficient for full range (down to 16Hz) operation. The two other channels used 2 X 6BQ5's each and the OPT was in the 1.5 pound range. This would not be sufficient for low bass operation. There was a choke in the power supply too. It was rather small. All amplifiers used fixed bias developed from another transformer winding and a silicon rectifier.
I tried the power transformer with a Simple P-P amp but the B+ was only 300 volts which isn't quite enough for cathode bias and power levels over 12 WPC.
It is interesting to note that 7 of the 8 output tubes are the original Baldwin branded Sylvanias. I popped 4 of them at random into a Simple P-P and they had no problem cranking out 30 WPC with 400 volts of B+, 350 on the screens. Low distortion and no red glow to be seen, just a little blue on the glass. Most current production tubes glow brightly at this power level (except JJ's).
Ok, merry Christmas and all that - I've had a bottle of reasonable Chardonnay with dinner (some in the stuffing, and the rest in me), so I'm feeling about as charitable as I'm going to be.... Anyway, I've done some figure of merit measurements on a cheap Edcor P-P output transformer and a pair of toroidal power transformers with the idea of employing one of these guys as a 50% tapped autotransformer for phase inversion duty. I used a variac and a couple of DVMs to do volt-amp measurements across the transformer primaries to calculate primary inductance at a reasonable level of primary excitation.
First up - the Edcor XPP-8-8k cheapo transformer from Edcor. Using a variac and a couple of DVMs, I got 50 VAC, 0.53 mA AC as a plate -to-plate measurement. This calculates (assuming 60Hz Yankee mains frequency) to 250 H plate-plate, or 62H plate-center tap inductance - not bad for a cheap transformer.
A small 18V surplus toroidal transformer yields 0.46 mA. 50V across its primary windings - this calculates out as 288H across the entire winding, or 72 H to the center tap - not bad for a little transformer that cost almost nothing.
A third measurement was taken from a somewhat larger toroid I bought a while back from All Electronics - the measurement was 50 VAC/0.39 mA, or 340 H across the whole winding, 85 H from one side to the center tap.
It looks like any one of these would serve as an interstage transformer based on simplistic primary inductance measurements. Winding-winding leakage and primary volt-second capability will also play a role, of course. At any rate, these are all cheaper than Jack at Electra-print charges for his autotransformers, which turn out to be not all that expensive, either. Still, a bird in the hand, and all that...
I'll try an amp based on one of these transformers, with the option of upgrading to the Electra-Print autoformers at a later date.
First up - the Edcor XPP-8-8k cheapo transformer from Edcor. Using a variac and a couple of DVMs, I got 50 VAC, 0.53 mA AC as a plate -to-plate measurement. This calculates (assuming 60Hz Yankee mains frequency) to 250 H plate-plate, or 62H plate-center tap inductance - not bad for a cheap transformer.
A small 18V surplus toroidal transformer yields 0.46 mA. 50V across its primary windings - this calculates out as 288H across the entire winding, or 72 H to the center tap - not bad for a little transformer that cost almost nothing.
A third measurement was taken from a somewhat larger toroid I bought a while back from All Electronics - the measurement was 50 VAC/0.39 mA, or 340 H across the whole winding, 85 H from one side to the center tap.
It looks like any one of these would serve as an interstage transformer based on simplistic primary inductance measurements. Winding-winding leakage and primary volt-second capability will also play a role, of course. At any rate, these are all cheaper than Jack at Electra-print charges for his autotransformers, which turn out to be not all that expensive, either. Still, a bird in the hand, and all that...
I'll try an amp based on one of these transformers, with the option of upgrading to the Electra-Print autoformers at a later date.
Great article on transformers ...
Wrenchone -
In another thread I was directed to the following excerpt from the Radio Designers Handbook. It has some great info on autotransformers and what they do ...
http://www.gyraf.dk/schematics/RadioDesigners Handbook - Ch.5 - Transformers.pdf
Wrenchone -
In another thread I was directed to the following excerpt from the Radio Designers Handbook. It has some great info on autotransformers and what they do ...
http://www.gyraf.dk/schematics/RadioDesigners Handbook - Ch.5 - Transformers.pdf
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