:Hello. I'm trying to revive an old Trutone model D1846. The output transformer was obviously tinkered with by a previous owner. The schematic shows that the input resistance should be 450 ohms and mine reads 448 ohms, close enough. However, the output side reads .8 ohm and the schematic says it should be 3.5. I'm thinking it's shorted, correct? It is marked 51X134-A and 10 S 47 (the "S" has a T and c inside it) on the top. Any ideas where I might find a suitable replacement? I've searched the web and asked at local electronic suppliers with no luck. Thanks in advance.
:Sounds like a Stancor transformer and it may be just fine. DC resistances alone don't tell the story. Does the set work and sound OK with this transformer? If so, no need to replace it.
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When you do check the tubes, don't replace any that just show Weak. Need to troubleshoot first in a systematic manner - by checking voltages at each tube.
Doug
:When you measured the resistance of the secondary winding, did you disconnect it from the speaker voice coil?
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:When you do check the tubes, don't replace any that just show Weak. Need to troubleshoot first in a systematic manner - by checking voltages at each tube.
:Doug
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Robin:
Tubes are funny animals, those that test "weak" will often work just fine. I think your transformer is fine. You need to inject some audio into the grid of the first AF amplifier. This can be done by touching the high side of the volume control with the volume at max. You should hear a speaker rattling buzz. If you do, the audio is ok for now, we'll worry about distortion and such later. Also, I would do an oscillator check about now, take a radio known to be good, tune it to a quiet spot in the upper half of the broadcast band, and tune the suspect radio back and forth around 455 kHz below the good radio. At some point, you should hear the local oscillator in the good radio.
Keep in touch,
Lewis
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::When you measured the resistance of the secondary winding, did you disconnect it from the speaker voice coil?
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::When you do check the tubes, don't replace any that just show Weak. Need to troubleshoot first in a systematic manner - by checking voltages at each tube.
::Doug
:Hello. I'm trying to revive an old Trutone model D1846. The output transformer was obviously tinkered with by a previous owner. The schematic shows that the input resistance should be 450 ohms and mine reads 448 ohms, close enough. However, the output side reads .8 ohm and the schematic says it should be 3.5. I'm thinking it's shorted, correct? It is marked 51X134-A and 10 S 47 (the "S" has a T and c inside it) on the top. Any ideas where I might find a suitable replacement? I've searched the web and asked at local electronic suppliers with no luck. Thanks in advance.
:Robin...I just restored a Trutone model D696D...I recaped it and slowly brought it up on a variac...With-in a few mnts the transformer was getting VERY warm...so I new there was a short somewhere...went through all under chassie and could not find the problem...I said to myself..."dam it..bad transformer"..so I de-soldered all wires from under chassie and took transformer apart. I took all leads and put heat shrink on them..Was just a hunch..but I though the leads were shorting out where they came out of transformer. Sooooooo I reamed out the hole in transformer casing... twice as big..re-inserted transformer ...and woollllllah ..the dam thing came to life...
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::Hello. I'm trying to revive an old Trutone model D1846. The output transformer was obviously tinkered with by a previous owner. The schematic shows that the input resistance should be 450 ohms and mine reads 448 ohms, close enough. However, the output side reads .8 ohm and the schematic says it should be 3.5. I'm thinking it's shorted, correct? It is marked 51X134-A and 10 S 47 (the "S" has a T and c inside it) on the top. Any ideas where I might find a suitable replacement? I've searched the web and asked at local electronic suppliers with no luck. Thanks in advance.
His radio is manufactured by Truetone also and had a transformer issue. Perhaps he is suggesting to Robin to check the output transformer for something similar? The transformers are undoubtedly different in construction so my personal feeling is that it is not the issue with Robin's, but I believe this to be the correlation.
(OMG did I just validate a posting by G.Berg?)
Both primary wires on an audio output transformer will have almost the same voltage. You won't read any voltage on the secondary. Best to make sure primary winding isn't open. Secondary will be ok. It's heavy wire.
Norm
: Tube tester arrived today. Yay! I went to Radio Shack to look for some caps but the selection was poor to say the least. They don't even stock bare speakers. Well, all tubes test fine but when I checked the voltage on the output transformer I got 265vdc going in and zippo coming out. Any idea what I should be getting? If the trans is bad, any idea what to replace it with? I don't have any junk radios around to scrounge from yet.
Hmmmmm. . . .’dat do be one big ‘ole puppy ! Aye-emming, Eff-emming and Pony–graffff capabilities , no less. . . . .to boot !
In the beginning:
No, the tubes light but I get no sound except static when switching bands. I have a tube tester coming in the mail next week but right now I'm just trying to see if I have proper power to all the transformers. .
If you are getting static and band switching clicks, seems like that you are both having your power supply getting B+ to the AF output stage and also that there is connection being made between the output transformer and the plate circuit of the output stage and then even getting all the way through to the speaker.
As for the measurement of B+, what’s the chance that you made an error in tube socket referencing in counting out the pins…E.G. top chassis view vice bottom chassis view. Trace down the blue wire from the AF output transformer that goes directly to the plate # 3 of the 6V6 in order to be sure, but with those speaker pops, seems like that route certainly has to be intact.
Well, all tubes test fine but when I checked the voltage on the output transformer I got 265vdc going in and zippo coming out.
Then in your final post you say:
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Where is that point of measurement being taken ? .. . .Could that be due to not tracing down the output transformers blue plate wiring as mentioned ?
If that turns out to be OK a good dynamic testing of the whole audio string and its acoustics can be enacted by taking anywhere from .001 upwards to .1 ufd paper /or/ ceramic capacitor at hopefully 600 VDC rating, but a 400 might do if that is all that can be found.
(My consideration, being that your cupboard is quite bare !)
Run the volume control down to minimum volume position and clip lead connect one lead of the capacitor to the high end of the volume control. That would be the top connection shown at the top of the schematics volume control legend shown as R-17 and is also sharing a common connection with the C32 68 mmf capacitor and even the common wiring that goes to the left to the #1 terminal of the function selector switch..
That then leaves the other lead of the sub capacitor to go to another clip lead and connect to the plate connection #3 of the 6V6.
If you will the power up the set for warm up and then bring up the volume control setting gradually, you should find yourself with a variable frequency power oscillator if the stages from the volume control all the way to the speaker are actually receiving their power and operating properly.
If that is working, then one needs to disconnect that test rigging and be prepared to troubleshoot from the volume control forward in that circuitry.
73's de Edd
