New proect! 1953 Hoffman Television Super Receiver Mark V Tv Phono Radio Console

[Yamamaya42]

Sadly, the power transformer in the radio section is very VERY dead...

https://i.imgur.com/sS6609i.jpg
https://i.imgur.com/mznGDhX.jpg

Which makes finding service info for it all the more important.

[Electronic M]

Is there a chassis number for the radio in the set, or a 'see this folder for radio' note in Sam's?
If not you could search radio consoles by that brand on the radio museum website and look for a radio with a similar face and tube compliment.
If the radio and TV don't share power supplies/audio output stages then it's almost a guarante that there was a radio (or radio/phono) only version sold.

[Yamamaya42]

Originally Posted by Electronic M

Is there a chassis number for the radio in the set, or a 'see this folder for radio' note in Sam's?
If not you could search radio consoles by that brand on the radio museum website and look for a radio with a similar face and tube compliment.
If the radio and TV don't share power supplies/audio output stages then it's almost a guarante that there was a radio (or radio/phono) only version sold.

Can't seem to find it on RM

11 tubes
5U4GT
6V6G2 X2
6BA6 X3
6SN7
6BE6 6SQ7
6AL5
unmarked tube 12AT7 perhaps


https://i.imgur.com/H75zSH9.jpg

https://i.imgur.com/ZaPPZgw.jpg

https://i.imgur.com/a2j1pCY.jpg

No mention of the Radio in the SAMs, and nothing but a serial # on the radio chassis :/

I would not have thought it would be so hard to find info for the radio part

[Yamamaya42]

Granted, I am getting a bit ahead of myself, as I will be focusing on the TV part first, and this will take a while, but there is no audio output in it and it needs the radio working for sound.
The Hammond 290AX Power Transformer SEEMS to be the right type for it, but as in the TV, the radio also has failed candohm resistors, all burned and opened, it looks like they are what started the problem, they shorted and toasted the transformer to the point that it arced out, it looks like it almost caught fire in there, there is so much carbon.


If I can't find info on the radio ( or be pointed to where to find info ) in the time while working on the TV, I do have this to fall back on.

https://i.imgur.com/zE38A3N.jpg
the radio from the FADA, which is sort of the same. :/

[Yamamaya42]

did someone order a power transformer? extra crispy!

https://i.imgur.com/5mWpYbY.jpg

[old_tv_nut]

eek!

[Yamamaya42]

here is a close look at the damage under the 5U4 socket and candohm1.
https://i.imgur.com/il1O5tw.jpg
gonna need a new socket.

i removed it and took it apart.
https://i.imgur.com/HsRbW5s.jpg
TOAST
there is no info on aside from a Hoffman part # and who made it for them, LONG gone...
in the FADA radio like it, in that position the resistor is 47 ohms. but THAT setup has a filter choke where 42 ohms, this has none, and in the place where candohm2 in the Hoffman, the FADA has a 5.5k.

If i cant find info for this and go this way as done in the FADA, i may have to up the values a bit to adjust for there being no filter choke.

[Yamamaya42]

Correction, The transformer needed is Hammond 290CX not 290AX :O
They are pretty much the same, except for that the CX has 2 more amps on the 6.3v heater winding than the the AX, and when I added all the tubes up, it was too much of a load for the AX having only 2.25A, the CX has 4.5.

Took apart both candohm resistors, the 2nd one is mostly intact, (still bad) and seems to be about 3k, or used to be, which is very close to what is in the FADA Radio schematic (3.3k) at that point.
So, making a guess of 3-3.3k 10w chassis mount resistor for here?

Candohm 1 is completely destroyed, burned and blackened, wire on it broken in many places, looks like it was arcing.

For this, I will just have to see what works, 50/70/100 @ 10w.

There is always some give and take in tube stuff, so it should not be hard to get this going if no info on it can be found.

It's pretty clear what happened to it, capacitor failure, plus lack of fuse protection, this coupled with the fact who ever was using it was not paying attention to it and let it burn up.

Evident by the cathode capacitor for the 6V6GT has exploded, and it's paired resister is burned out.
This caused bias to raise above normal and stress already weak electrolytic capacitor,which shorted, overloading the Candohm which shorted and took out the transformer, had the makers put a fuse in there, this chain would have been broken.

Oh well.

Mouser is about to ship the parts for the TV chassis.
So I can get a start on that, at least.

[Tom9589]

The first TV I ever worked on professionally was an RCA portable. The owner had allowed a beer to spill down the back which found its way into the power transformer. It looked like the power transformer out of this radio Yamamaya is working on. Fortunately, the electrolytics and the power resistors were OK. I also had to replace the safety glass. There was a circle shaped indention in the safety glass which roughly approximated the bottom of a beer can. Hmmm.

[jr_tech]

“ cathode capacitor for the 6V6GT has exploded, and it's paired resister is burned out.”

Imho, a shorted or gassy 6V6 might have started the whole unfortunate chain of events

jr

[Yamamaya42]

FOUND IT!!!!
SAMMs 221-6
however this Set seems to be a hybrid... :O

I look up the chassis number on the sticker on the back of the unit and get pointed to SAMs 201-5
which has just the TV, and pretty much matches.
But just by sheer luck I found the combo 221-6 which has the radio and phono, TV is almost the same, slight differences.

Weird.
It says candohm 1 500 ohms 7.8 watts, candohm 2 2.6k 6.5 watts.

Transformer
sec1
695vct .130ADC
sec2
5vac 3A
sec3
6.3vac 3.7A

Hammond 290CX specs
650/550Vct @ 100 mA
Secondary 3 6.3Vct @ 4.5A
Secondary 4 5V @3A

[Yamamaya42]

https://i.imgur.com/FWTzNOB.jpg
https://i.imgur.com/ArZ74fk.jpg

all prepped and ready to haul upstairs to my work room!

A bit of more good news for the Radio section, now that I have the Sams, i was able to check the Audio output transformer , and it seems OK, it says DC resistance @ 380 ohms and my DVM says 355, so I guess it was not damaged!

[Yamamaya42]

I do wonder about the strange white stuff that I saw on the FBT, not seen that before.

But as mentioned, the general resistance check seemed OK going by what was in the SAMs, just not sure what to make of it.

Just wait till I get horz/HV up, see what happens?

Give it a good deep coating of super corona dope and then try?

Whatever that white crud is, I'm kinda afraid to touch it for fear of causing unneeded damage, but I don't think a few layers of SCD would hurt.

And if all fails, and the FBT is problematic, ETF does have 3 compatible replacements.

[Yamamaya42]

some more good news,
I MAY not have to buy a power transformer

this MAY work.

https://i.imgur.com/pteUqEl.jpg

[Yamamaya42]

restoration started.

https://i.imgur.com/UcO6drS.jpg
before

https://i.imgur.com/0eEXVCG.jpg
after
notice the exploded bumble bee :O

https://i.imgur.com/VC2A2bR.jpg