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

[Yamamaya42]

Originally Posted by Electronic M

If there's an AM loop antenna in the cabinet it may need it to perform good on AM...FM also may benefit from an antenna but it usually doesn't need that much wire to make FM happy.

It does, but I'm sure there is bum resistors, like the 68 ohm cathode resistors that i seem to always find bad

Also, I need to balance the outputs, one tube is running a tad bit hotter, this I'm sure because I have not replaced the G1 resistors yet 470k to gnd one tests pretty close, the other at 525k not TOO bad, but it prob explains why that tube is hotter.

I was focused mainly on fixing the broken blown transformer and replacing caps and getting it working, looking for bad resistors is next.

BTW, I saw your video about the phones, your workspace is about as clean as mine!

I have an old telephone magneto that I got from my grandpa long ago, I doubt many know how much fun you can have with them!

[Yamamaya42]

Well, it ran for a while, then it stopped.

The cheapy China 500 ohm 10W resistor that was in there ( which I doubt was really 10w) burned open.
It was replacing a resistor rated at 7.8W, and the silly thing was sitting on the side of the chassis, but it still could not take the strain, I have another one, but I doubt I will put it in, cause it seems more like a 5W to me due to its small size, and the just over sold the rating.

I have the 600 ohm 10W in there now, and it seems fine, still just as loud, and it does seem to be a REAL 10W one, https://www.mouser.com/ProductDetail/71-RS10-600

As for the 2.6k power resistor, I could not find one in the exact rating needed, so I used, https://www.mouser.com/ProductDetail/279-THS101K5J & https://www.mouser.com/ProductDetail/588-40J1K1E
both rated at 10W the original being rated 6.5W.
I doubt that they are being pushed to the limit.
Where as the chassis mount resistors were tacked down to help cool them, there is no real way to do that to the other kind, unless thermal cement is used, but is such a thing needed?

[Yamamaya42]

Amp still OK, but no radio.

It does get rather toasty!

Even the 5u4gb with just heaters running gets quite hot.
Not sure if the tuner tubes are good or not at this point, but since the main goal was the TV section, not sure if I want to put in all NOS ones just to try to get it up.
I did not have any 6BA6 tubes that it uses 3 of ( AM RF AMP, 1ST & 2ND AM/FM IF AMP), so I stuck in 3 NOS 6AU6 which is said to be a sub, also a NOS 6AL5 ratio det.
Made no diff whatsoever.
The 6SQ7 AM DET AVC 1ST AF AMP is prob OK, cause amp is working fine.

Unknown
12AT7 FM RF AMP/ MIXER
6BE6 FM OSC AM CONV

I'm just going to have to methodically go over every resistor in the radio section this weekend and see what I find before I think of getting any NOS tubes for it.
A quick check showed plate voltages to be a bit high, by about 55v in the radio area, but normal in the amp.
Not sure if this is due to weak/bad tubes or bad resistors or both.

[Yamamaya42]

OH YEAH!

https://i.imgur.com/1fCV2DL.jpg

bad resistors !


That SHOULD BE 56k....
and the unreadable one under it, should be 1m tests at 1.6m

no wonder the damn thing dont work!

[Yamamaya42]

have only found 3 really bad resistors, but replacing them has not helped.

new tubes on the way
6BA6 1st/2nd am/fm IF and AM RF amp, 6BE6. FM OSC and AM conv. and 12AT7 FM RF AMP/MIXER.
if this does not get the radio working, I will just give up on it. as the TV was the main goal anyway.

[vortalexfan]

Originally Posted by Yamamaya42

have only found 3 really bad resistors, but replacing them has not helped.

new tubes on the way
6BA6 1st/2nd am/fm IF and AM RF amp, 6BE6. FM OSC and AM conv. and 12AT7 FM RF AMP/MIXER.
if this does not get the radio working, I will just give up on it. as the TV was the main goal anyway.

If I would of known you needed some tubes I had a whole ton of 6BE6 and 6BA6 tubes as well as a bunch of 12AT7 tubes that all test like brand new yet (they were pulled from radios that I was unable to get going electrically but the tubes were still good) that I could of sent you a couple of each for the cost of shipping.

But anyways it's good to hear you're making progress with this radio.

I'm curious is this the same unit as the one Shango has that he is planning on working on in one of his future videos that he picked up in one of his TV pick runs?

[Yamamaya42]

Originally Posted by vortalexfan

If I would of known you needed some tubes I had a whole ton of 6BE6 and 6BA6 tubes as well as a bunch of 12AT7 tubes that all test like brand new yet (they were pulled from radios that I was unable to get going electrically but the tubes were still good) that I could of sent you a couple of each for the cost of shipping.

But anyways it's good to hear you're making progress with this radio.

I'm curious is this the same unit as the one Shango has that he is planning on working on in one of his future videos that he picked up in one of his TV pick runs?

sort of, but 5 years newer, with a 21 rectangle CRT, but made very much the same way.

[vortalexfan]

Originally Posted by Yamamaya42

sort of, but 5 years newer, with a 21 rectangle CRT, but made very much the same way.

OK, I was wondering about that, because I know Hoffman was an L. A. area manufacturer that seems to come up a lot in Shango's videos (another brand is Packard-Bell.)

[Jeffhs]

Originally Posted by Yamamaya42

have only found 3 really bad resistors, but replacing them has not helped.

new tubes on the way
6BA6 1st/2nd am/fm IF and AM RF amp, 6BE6. FM OSC and AM conv. and 12AT7 FM RF AMP/MIXER.
if this does not get the radio working, I will just give up on it. as the TV was the main goal anyway.

Is the radio working at all, or is it completely silent? If it is still silent after you replace the tubes you mentioned, I would check one more thing before giving up: the antenna connections. If these are disconnected or the antenna itself has a poor or outright open connection, your set's radio will not work at all, unless you are in an extremely strong signal area, and even then you may receive only a small number of stations. However, as I said, the first thing I would do would be to replace the three tubes you mentioned, as one of them may be weak or burned out. If any of the tubes you mention are defective in any way, you will either lose reception altogether or, if you hear anything, the signals will be very weak and noisy.

The radio in your Hoffman console should work very well, as the set was made in 1953, when not every city or town in the United States had local radio. Because of this, the sets had to be, and generally were, built for DX (reception of radio stations located some distance from the set's own location); this is why I say the radio in your console should, indeed must, work almost exceedingly well. In radio's very early days, the first sets were crystal sets with no amplification, so a very good antenna had to be used in order to get any reception at all. My first crystal set was hooked up to a 50-foot (more or less) long-wire antenna and received one local station located only a mile or two from where I lived at the time. However, I will never forget one night right after that station signed off for the night (it was a 500-watt daytime-only operation in a Cleveland suburb). I heard the local station sign off, then, to my dumbfounded surprise, I heard, very weakly, one or two local Cleveland stations in my headphones, one on top of the other (crystal radios are anything but selective).

[Yamamaya42]

Originally Posted by Jeffhs

Is the radio working at all, or is it completely silent?

completely silent.

both AM/FM

though slight hiss heard in FM, and when I tap the FM aunt terminals with something metal I get some kind of sound change.
tubes will be shipped snail mail mon/tue

[Jeffhs]

Originally Posted by Yamamaya42

completely silent.

both AM/FM

though slight hiss heard in FM, and when I tap the FM aunt terminals with something metal I get some kind of sound change.
tubes will be shipped snail mail mon/tue

That's good to know. I hope the new tubes get your Hoffman console's radio working again. If you can hear a slight hiss on FM, and you hear a slight change in that hiss when you touch the FM antenna terminals with a screwdriver or anything metal, all is not lost.

As I said, the new tubes should restore normal operation; if not, I don't know what else could be causing the problem. If there is no reception on both AM and FM, and new tubes do not get things going again, the problem must be in a part of the radio (other than tubes) which is common to both bands. I've been away from electronics too long (I had to give up my workshop when I moved from my former home to an apartment over 20 years ago) to be able to offer any further advice.

[vortalexfan]

Now the interesting thing is that I had a late 1940s vintage Westinghouse AM/FM Radio (a Model H-1821) that had a similar problem (no signal being picked up on either AM or FM) and I tried replacing several of the IF, RF and Audio tubes and even recapped and replaced all out of tolerance resistors and nothing fixed the issue, (I suspected that either one of the oscillator coils was bad or a bad antenna coil or maybe a bad IF can, but either way the radio was a total loss so I just salvaged the cord, pilot light and the tubes from the unit and scrapped it out, because if it was one of the IF cans or coils that was bad there was no way I would of found replacements for it as they were an oddball style of coils and cans.)

So with that in mind, and I hope that isn't what's wrong with your radio, but I would check the antenna or oscillator coils first and then if those check out then check the IF cans.

[Yamamaya42]

I'm still tending to think (hope) that it's a symptom of bad/weak tubes, all I can tell is that all the general voltages in the RF/IF area are there, but 50-55 volts higher than shown in the schematic.

If there was an open coil, there would be a missing plate bias, and all are there.
YES, the power supply has been changed due to the burn out, but I doubt that is the problem here.

300acv tap is being used, rather than 340v original, 1kv 1a silicon diodes rather than 5U4GB, first resistor in voltage divider changed from 500 to 600 ohms.

Amp section working flawlessly.
Even if I lower the main input to 70-75v, it makes no difference, Amp still happy, raidio quiet.
USPS says the ordered ones will be here in 2 days, will just have to keep fingers crossed.

Shame that I don't have easy access to a tester here,

[Electronic M]

In my experience RF/IF stages usually work better with excessive B+... About 5 years ago I got a trio of Sherwood tuners and one had one had a dead power transformer...I cobbled up a replacement but had ~50V too much B+ IIRC. It worked NOTICABLY better than the stock one.

[Yamamaya42]

Radio is alive!

https://www.youtube.com/watch?v=lje6Zb-WLv8

it WAS bad tubes!

namely the 6BE6.

It's quiet easy to push this little amp into clipping, not that I expect much from this hoffman made thing.
15 amps max.
It was not made to do very much