Baldwin 51P to Fender 5D4

[jonathan_kea]

A couple of years ago, I made a routine trip to the dump, and someone had pushed a Baldwin 51P tube organ into the metal pit for recycling, wood, keys and all. I immediately grabbed my attention because of the two 8" speakers and about 60+ 12AX7's! I jumped in and started pulling tubes when the attendant came up to chat. $20 later, and he had forklifted into the back of my truck. I got it home, plugged it in, and it still worked. It made me somewhat nervous as it felt very leaky and actually made the hair on the back of my neck stand up.

I pulled the chassis, speakers, baffle, and disassembled the wood parts to use as a cabinet later on. It uses two 6L6's in the output stage. I am thinking about using these components to build a 5D4 Super, as it seems relatively simple and I can use the existing power supply and amp chassis (sans the 60+ tone generator 12AX7 component) to build it point-to-point.

I've attached the schematic and a close-up of the power supply. The 5D4 calls for 370V B+, and the Baldwin appears to supply 350V B+ at C1. Is this a suitable power supply for a 5D4? Also note that the Baldwin has a substantial choke between C1 and C2. Should I retain the choke? Thanks in advance.

[sluckey]

I would keep the power amp and power supply, including the choke, just as is. All you need is to add a preamp of your choice.

[jonathan_kea]

Wow! That’s awesome- thank you.

[jonathan_kea]

sluckey - just for edification, what do A, B, and C represent?

I think A goes to the 1st filter cap, and B and C go the 2nd filter cap (on the other side of the choke).

[sluckey]

Node A is the first filter cap, B is the second filter cap, and C is the third filter cap. The Baldwin amp has the PI being fed from the second cap, but I moved the PI to node C like the 5D4 shows.

[bmccowan]

A couple of years ago, I made a routine trip to the dump

Several years ago my town got rid of the dump. It was a sad day.
Great project!

[jonathan_kea]

sluckey - there were 3 or 4 large green ceramic resistors downstream in the power supply that I believe were required by the tone generator section of the organ. I have removed those from the schematic. Is this what you envisioned? Also, should I use the 5D4 (10k) spec for the resistor between node B and C?

[sluckey]

That's it. I would start with a 10K between nodes B and C, but be prepared to adjust up/down as needed. Can you post the entire Baldwin schematic?

[jonathan_kea]

Struggling to get this down to a decent resolution under 1024K. Let me know if this works. There is also a schematic for the pedal percussion section with a preamp and all the crazy organ sounds.

Also, check out the neat vibrato circuit that uses a small transformer. Might bring that into the circuit as part of phase 2.

[sluckey]

Ouch. Hurts my eyes.   

[jonathan_kea]

Let me try a couple of things... they scanned it at really high res at fedex...I had blown them up to poster size to try to make sense of it.

[jonathan_kea]

This one should let you zoom in reasonably to get the details.

[shooter]

maybe
really like the draftsmanship through

[jonathan_kea]

Wanted to modify the 5D4 input circuits to reflect a single input.... Does this look correct with volume & tone?

[sluckey]

No. You cut out the wrong part.

[jonathan_kea]

How does this attempt look?

[jonathan_kea]

oops, looks like I left the plates connected in the 12AY7 - I would remove that connection in practice to use 1/2 the 12AY7

[jonathan_kea]

updated schematic...

[sluckey]

updated schematic...

That works. However, since you now have an extra triode may I suggest to parallel them...

[jonathan_kea]

Neat! Will that provide extra gain vs the single triode? Thanks again for all of your help on these projects!

[sluckey]

Some say it has slightly more gain and a fuller sound. I've never tried to measure it. Notice I changed the cathode resistor to 820Ω. If you decide to only use one triode you should change that to 1500Ω.

[jonathan_kea]

Will give it a shot - appreciate it!

[passaloutre]

@jonathan_kea

I just picked up a Baldwin 51P, and I was wondering if you could email me the full resolution schematics you have