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Old 10th June 2010, 09:48 PM   #1
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Default Baldwin Transformer Swap

I've been collecting organ iron for use in building experimental P-P amps. Baldwin has an interesting amplifier that uses PPP 6BQ5s with a substantial output transformr. I nailed down two of these transformers on E-pay with the intention of wrapping an amp around them, but it turns out that there are two design revisions of this amplifier that use different transformer impedances. One transformer I have measures out as 5k plate-plate impedance for an 8 ohm load, and the other is 3.5k impedance for the same load. I would like to have two 5k transformers. Does anyone have one of the 5K Baldwin transformers they'd be willing to sell or swap? For reference, the P/N on the 5k transformer I have is C512 023668A. The 3.5k transformer is C512 025347.
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Old 11th June 2010, 02:05 AM   #2
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I've got an output transformer from a PPP 6bq5 Baldwin amp that I recently dissected. A quad of 6bq5s (two per side) and 3 12ax7s for the main amp and an attached section of 2 12ax7 and 2 6bq5 that drove a leslie cab. The number on this one is C512-028812A which doesnt match either of yours. Different production run? I will test it for impedances.
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Old 11th June 2010, 02:18 AM   #3
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Just measured it and it seems to be a 6.5K primary unless my math is off. 12 volts on secondary reflects 398 on the primary, divide pri. by secondary to get voltage ratio, square of ratio multiplied by 8 (8 ohm secondary) is approx. 6.5K, Does this sound correct?
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Old 11th June 2010, 03:07 AM   #4
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I dissected a 3 channel Baldwin organ amp. It had two P-P channels running the original Baldwin branded Sylvania 6BQ5's and a third channel that had 4 X 6BQ5's in PPP. I will try the small OPT's in something small some day since I have a matched set. The big transformer is probably in the 3 to 4 K range since it was used with 4 X 6BQ5's. The number on it is C512-025947. Could your 3 be a 9? I have made no measurements on these transformers, but I really don't need the odd one, so you can have it for the shipping costs if you want. PM or email me.
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Old 11th June 2010, 04:14 AM   #5
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I've got a Baldwin chassis here on the floor,mono,PP 6L6's. Primary impedance is approx 6.4K:8ohms. Number 512-19234A.
(just a bit more Baldwin info for the thread/future searches)
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Old 11th June 2010, 06:08 AM   #6
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I have several flavors of Baldwin iron at present including several types of 6L6 and 6BQ5 transformers. A pair are going into my "Lil Devil" amp. I characterize all of this iron by using a sine wave power source to drive the primary through the plate-plate leads at 50V, 300 Hz. I monitor the output using a DVM and monitor the input current using a Yokogawa WT-210 power meter. From the input current reading I can calculate the primary inductance under high level excitation, and from the output volts I can get the turns ratio, and hence the output impedance, assuming an 8 ohm load. This is how I got the readings on the PPP 6BQ5 transformers I have so far.
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Old 12th June 2010, 03:10 AM   #7
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Quote:
A pair are going into my "Lil Devil" amp.
You might try a certain pair of rusty OPT's. They sound far better than they look. I have used a pair on many of my red board experiments.
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Old 12th June 2010, 04:04 AM   #8
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The "rusty pair" are too large to fit into the 6" cube that is the basis for the "Lil Devil" (besides, the holes are already drilled for the other transformers) . They will be saved for a larger (and nastier) amp to be defined.
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Old 25th June 2010, 09:50 PM   #9
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George - You were right, the number on the 3.5k revision of the Baldwin transformer is indeed C512 025947A. The number stamp on my 3.5k transformer is faint/half-done, and the "9" looked like a "3" as a result.

I just got the complete hunk of amplifier that this iron came from, and it's a monster, with a power supply transformer of heroic dimensions, the aforementioned transformer on top along with a choke, and two more transformers underneath the chassis. I've got half an inclination to pick another one of these up in complete form and use it as the basis for a bi/triamplifed system. There's room enough (and more than enough power) for an electronic crossover underneath. There's also plugs for powering other chassis, and a pair of 5U4Gs. Just what I needed, another project...

Last edited by wrenchone; 25th June 2010 at 09:51 PM. Reason: sp
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Old 25th June 2010, 10:08 PM   #10
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Quote:
with a power supply transformer of heroic dimensions
Yeah, I smiled when a friend was tossing that one in the trash. He is a SS kind of guy. I would have preferred a bit more B+ voltage but for free.....

I gutted the entire amp. The original Baldwin branded Sylvania 6BQ5's crank in a Simple P-P at over 400 volts. I plan to at least try the little OPT's in a 6AQ5 amp, and I always keep chokes, but I don't have a use for the 3.5K transformer since I have plenty of the "rusty" transformers, without the rust and they work fine at 3.3K. If you want it, I will send it for the cost of shipping.

Quote:
Just what I needed, another project...
Sherri and I have come to realize that we each have more projects than we have life left, and we are paying to keep them. SO.... That is why the complete Baldwin amp, and several Magnavox amps, became a box full of transformers. Sad to say several amps, radios, and other stuff went directly to the metal scrap guy.

No one seems interested in the 1500 volt 1/2 amp power supplies either, so they are destined for the recycler.
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