I have a Baldwin Professional that has "smoked" two of the six (6) R47 wires that are soldered on the lugs bolted across the rear of the heatsink of the TO-3's. What is going on? and what would replace them with?(after I fix the problem).
A knurled nut & 8-32 bolt fell out from where it was wedged between the Ch.2 board and the chassis (Ch.2 had not worked before - zero/nada). Now both channels "work", but are weak & distorted.
Quote from: clguy on February 15, 2012, 08:44:24 PM
I have a Baldwin Professional that has "smoked" two of the six (6) R47 wires that are soldered on the lugs bolted across the rear of the heatsink of the TO-3's. What is going on? and what would replace them with?(after I fix the problem).
A knurled nut & 8-32 bolt fell out from where it was wedged between the Ch.2 board and the chassis (Ch.2 had not worked before - zero/nada). Now both channels "work", but are weak & distorted.
We'd need to see a schematic or at a minimum, some good pictures of the board, to help. Get us those and we'll help as best we can. :tu:
I have two TO3's with shorts (no resistance) from the emitter to case.
There is base & emitter voltage to the small transistors and output from all but the Ch.2 fed from the volume pot. (Jim002) and output board with orange dot (Jim001).
My attachments are not coming through. The schematic I had was baldwin_schematic.gif from Teemk on Sept.14,2008
Can I use 2 watt flame proof metal oxide power resistors to replace the blown 0.47ohm wires (fusible links)? Do I need more wattage like a cement ceramic?
Will Motorola MJ15004 or MJ2955 replace the shorted 36312 RCA's?
I think the 500uF 5WV in the output stage is shorted and want to use a 50 VDC to replace it.
There were 7 fusible links (.47R) on the rear of the amp. One was missing when I got the amp. I soldered in wires the same dia., turned it on and now have 3 smoked fusible links instead of 2!
Without the "wires" (=no smoke) the voltages seemed to check out (the first TO3 had +30 and the other 6 had +40).
The speakers may have been series wired (4+4=8). They were unplugged when I got the amp and I put white-on-white & black-on-black. Could this have lead to such a disastorous result??
I am now using my Kustom 4060 pa amp to play guitar (with the Baldwin 4 ohm speakers - one on each side).
The original wiring was 2 x 4 ohm speakers in parallel for 2 ohms total, so that was fine.
Problem is you have shorted transistors and being germanium they are both cr4p and very expensive.
If you dare, you can modify it for silicon , don't know your degree of commitment, *or* you can drop that power amp altogether and mount there 2 chipamps, each of them driving one speaker.
Post a couple sharp well illuminated pictures showing the full chassis both inside and outside to have a general idea of the available space.
Is the original amp built on perfboard or is that a homemade repair?
IMPORTANT: the PSU is not shown. It must be a simple circuit anyway.
We need to see it because we must rewire it to get +43V instead of those -43.
It should be no big deal but need the info anyway.
They already have +22V which must come from *somewhere*.
*or*, Plan C, you may also get a modern PSU; say, +/- 32 V, feed an LM3886 from it , which would drive the 2 speakers in series (50 excellent Watts into 8 ohms total) *and* still feed the preamp.
Be careful with your Kustom 4060; you are loading it with 2 ohms total, I doubt it'll like that. Use these speakers in a single cabinet and *always* in series or you´ll needñlessly blow the best part of what you habe: 2 original unreconed (so far ;) ) Vintage Jensens.
Hey !! I would sell these for good $$$ to Vintage lovers and buy 4 modern ("less desirable" ) Eminence legends or similar or 2 speakers and new guts for the Baldwin.
But if you burn them (easy to do) you have nothing.
I found an old schematic. It shows the NPN's with the 0.47 fuseable links across from the emitter to collector? Could the TO3 sockets or mica gaskets be causing the "short"? There is green (CU) on the connections.
Is an ASZ1015 a replacement for the old RCA TO3's?
I bought the Baldwin for the speakers. I needed a 4 ohm for the KPM4060's stereo amp (60 watts RMS @ 4 ohm). I am not sure I need to spend more time or money on the old amp but wanted to learn more and see if I could nurse it back to health.
Here is the schematic. It is hard to read and may be the single 12" model.
Dear clguy, your Baldwin speakers are not suitable for your Kustom KPM6040.
Sorry.
I found the schematic with voltages. I have no voltage at one side of the driver transformer to 3 TO-3's (beside the two germaniums that are shorted emitter/case).
The transistors (7) will be $50 including fusewire and shipping and the transformer $35 more.
Quote from: clguy on April 12, 2012, 06:32:03 PM
I found the schematic with voltages. I have no voltage at one side of the driver transformer to 3 TO-3's (beside the two germaniums that are shorted emitter/case).
The transistors (7) will be $50 including fusewire and shipping and the transformer $35 more.
Sounds like a good time to consider re-powering the amp with a chipamp circuit. chipamp.com has LM3886 kits that would do nicely.
Agree and add: *worst* case, if there is a wiring error or some other Murphy's Law manifestation, eaqch new LM3886 will cost a few dollars, and they are *always* available, while blowing those Germaniums again will bankrupt you.
Short time ago I repaired a very loud Behringer 2x12" combo which, go figure, used 2 x LM3886, each of them driving a 12" 4 ohm "Bugera" speaker, which (small World it is) is made by .... Jensen !!! Notice any similarity?.
Killer sound.
http://music-electronics-forum.com/attachments/18085d1334061834-behringer-gmx1200h.pdf (http://music-electronics-forum.com/attachments/18085d1334061834-behringer-gmx1200h.pdf)
Look at page 3.
If you decide to do this, you will have to mod the power amp slightly because they are meant for split supply and you have single supply (add some caps ) but nothing too difficult.
But *please* post a picture of how the power transistors are mounted, to check any heatsinks and available space, to see whether you can fit a new power amp there or not.
I have saved tons of "old/unrepairable" amps which were so either because of parts unavailability (germanium transistors or obsolete ICs) or because repair cost went above a used one on EBay, by "heart transplanting" a new power amp .
Sound remains the same because it comes "cooked" from the Preamp.
Thanks for the second look. I will use a chip amp to replace the output amp on the Baldwin.
The space where the capacitor/holey board/ output transformer was is 12" x 4" x 2" deep. The Channel 2 board with tremelo is on the other side and the Channel 1 is on the rear side to the left of where the new amp will be going.
I will need point to point instructions for hooking it up. The LM3886 can be purchased assembled with heat sink for under $20. The heat sink will stick out the back if
I think the schematic shows +43v (pin4) & -43v (pin11) or +32v (pin3) & -32v (pin10) from the existing Baldwin power supply on the bottom of the amp. The LM3886 wants 20-28v?
Will the old light bulb limiter be saved?
The LM3886 can use as much as +/-47v, but I wouldn't run it that hot. I'd shoot for about +/- 30-40v.
Here is the copy of the schematics from Arkansas and a picture of the output amp area. If I get the model with aluminum heatsinks they may stick out the back. If I get the LM3886 without the heatsink it may be bolted to the Baldwin's chassis/heatsink were the TO3's are.
Now that I look at the PSU, I'm thinking that there is a better way to use this amp.
The PSU (never seen it before) does supply + and - 43V.
They filter properly (2200uF x 50V?) the negative side, because they feed the power amp from it, but lightly (500uF x 50V) the positive side because they use it only for the preamp.
The regular LM3886 needs around +/- 30V or less so you have *way* too much.
To use it as the original amp, you would need to filter properly the +43V side (no big deal, just add a 2200 or 4700uF x 50V capacitor) *but* you must also mod the amplifier to work with a single supply.
It can be done, but it may confuse you, it's complex .
Tracks in the PCB should be cut, wire jumpers added, etc. *or* you would need to make your own special PCB . Complex.
Now I'm thinking about 2 options instead.
1) repair the amp "as is" but modding it for PNP silicon transistors instead of the PNP germaniums it used originally.
Least work, and probably cheapest too.
I've been googling around and this seems to be the preferred way to repair these.
A guy who did it offered to mail details, but his account is dormant since 2005 so ....
Anyway, I can calculate the value of the 2 resistors needed , no big deal.
I suggest you follow this path, fast and relatively cheap.
2) another option would be to straight mount there a regular discrete (sorry, too much voltage for chipamps) beefy power amp, which handles the +/-43V rails, and drives the speakers which should be connected in series to show 8 ohms.
Nice turbocharging but relatively complex and expensive.
I suggest you mod the original amp instead.
It's the solution used on VOX Thomas SS amps, same vintage, same outdated germanium technology.
Read this. Well, not all of it, but the part about going silicon.
I can calculate the bias resistor values for you, but will need a couple measurements from your actual amp.
www.geofex.com/Article_Folders/Thomas Vox/Thomas Vox Replacements.pdf (http://www.geofex.com/Article_Folders/Thomas%20Vox/Thomas%20Vox%20Replacements.pdf)
I'm answering in your *other* thread.
It gets confusing.
Please joecool join both threads into one.
Thanks.
The Thomas organ paragraph about TO3's (Output Transistors/paragraph 5) was the problem. The old TO3's grease dried out, two overheated and shorted. I need new mica washers and dielectric grease and maybe new sockets?
The premise of the article (Output Transistors/paragraph 1) is the old Germaniums are $20 each and matched pairs are hard to find. I can get them from "guitarampsky" for $50 with shipping (eight with a foot of fusewire.
I will still need a new driver transformer ($35 with shipping), even for the silicone replacement fix.
Well, Mr guitarampsky seems to have access to old original Baldwin stuff.
If that's so then probably you can rebuild it.
Remember to *always* use the lamp limiter and not connect any speaker until you are sure and have measured that everything is fine.
Go step by step.
Good luck.
Quote from: J M Fahey on April 18, 2012, 08:21:49 PM
I'm answering in your *other* thread.
It gets confusing.
Please joecool join both threads into one.
Thanks.
Done.