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 Post subject: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Sep Sun 24, 2017 7:02 pm 
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Joined: Dec Sun 22, 2013 5:03 am
Posts: 2318
Location: Santa Cruz mountains
Recently, our radio club in Alameda received a console radio as a donation. This in itself is not at all unusual; we seem to get those on an almost weekly basis.

However this one appears to be unique.....I mean really, really unique. The entire thing including the cabinet appears to be 100% homebrew.

Nineteen tubes spread out over three chassis. It appears to be a three band set (no FM). I forgot to get a picture of the cabinet, but it is nicely done.

The tuner chassis has three ranges: AM BC, Shortwave from 1.7 to 5.8 MHz, and Shortwave from 5.8 to 18 MHz. Two of the bands are penciled in on the National Velvet-type dial.

The audio amplifier seems to have great potential. push-pull 6V6 outputs with a hefty output transformer. There is a selector switch with the RIAA roll-off settings penciled on the chassis, so that kind of dates this unit as early to mid-50s. There is also a voltage regulator tube in the power supply, which is somewhat unusual for an entertainment radio.

There is a Webcor three speed changer mounted on rails in the cabinet, along with what appears to be a big Jensen Co-axial speaker.

The IF chassis has more IF transformers than I have ever seen in a non-FM tube radio. All of the IFs you see in the pictures below are 455Khz. There is a bandwidth selector and BFO, AVC, and ANL switches, like you would find on a decent communications receiver.

Some of our guys in the club wanted to gut it for the parts. I was not inclined to do that until I gave this thing a proper audition. Someone spent an awful lot of time building this, so it is worthy of at least a good listen before deciding its fate.

Initial power-up resulted in a huge amount of hum, according to the members that tried it. Filter caps are probably gone to heaven.

Tube complement:

TUNER CHASSIS:
6SG7
6SA7

IF CHASSIS:
6SJ7
6SK7
6SK7
6SG7
6J5
6H6
6H6
6H6
6H6

AUDIO AMP CHASSIS:
5U4
VR-150
6V6
6V6
6SN7
6SJ7
6SL7
12AY7

Here are pictures of the chassis:

Image

Image

Image

Image

Image

Image

Of course, there is no schematic available for any of this, So I'll be flying somewhat blind and relying on the competence of the builder and the notion that this did indeed work at one time. I would find it hard to believe that the builder would go to the trouble of making the cabinet if the insides weren't already de-bugged and tested.

Given the complexity of this setup, I'm a little skeptical that the original builder could have pulled the design for all this completely out of his head. It is an intriguing mix of communications gear and early Hi-Fi gear all in one unit.

I am wondering if the design for this came out of plans in an old magazine or book. Does this look familiar to anybody?


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Sep Sun 24, 2017 7:20 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2073
Location: Saskatoon
I'd be checking the old ARRL Handbooks from that era. My suspicion is that the builder didn't use any one single schematic for this, but probably took various sections from different schematics.

I notice that the IF selector switch has an "FM" position on it. I wonder if there was intended to be a second tuner built for the FM band. There's probably room for it on the tuner chassis.


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Sep Sun 24, 2017 9:09 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1513
Location: Canyon Lake, TX
It takes a very creative circuit designer to use four 6H6's in a receiver. I would love to see the circuit diagram for that thing.


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Sep Mon 25, 2017 4:54 am 
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Joined: Aug Fri 29, 2014 6:17 pm
Posts: 2351
Ed Engelken wrote:
It takes a very creative circuit designer to use four 6H6's in a receiver. I would love to see the circuit diagram for that thing.


That's what I was thinking, why all them diodes, but perhaps they're limiters for fm?


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Sep Mon 25, 2017 6:35 am 
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Joined: Dec Sun 22, 2013 5:03 am
Posts: 2318
Location: Santa Cruz mountains
I've started re-capping this.

Since the amp chassis also contains the power supply, I'm doing that first. The modern electrolytics you see in the picture below were replaced by me this evening. I'll finish this part come Friday when I have more time to work on it.

Image


The speculation about FM is interesting, but there is no way there is FM anywhere on this. The coil frequencies are clearly labeled in the RF and IF sections, and there are no VHF frequencies and no 4.5 Mhz or 10.7 MHz IF coils among them. There is FM penciled in on the selector, but I suspect that may have been a provision for an outboard FM tuner.


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Oct Tue 17, 2017 7:46 am 
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Joined: Jul Sat 23, 2011 9:33 pm
Posts: 792
Location: Long Beach Ms. USA 39560
Once upon a time some hams used Narrow Band FM (NBFM) to try to fight the static that bothered AM.
Looking at the top of the IF chassis, there are several cans between the tubes, it is probably bandpass filters using them. The filters would create narrow band for CW signal separation. They also could be conformed to detect NBFM. Check the switch wiring.
If the console was done as well as the chassis, it may be worth spending time to document and put into a museum.
They save welder's "creations" like weathervanes as art, this creation shows 50s art.
Use all three, the ARRL and Sams and Editors & Engineers radio handbooks and you'll probably be able to put together a composite schematic.
Thanks for not stripping it.

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Pat W5THT
Unhappy tubes blush while unhappy power FETs scatter plastic


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Oct Tue 17, 2017 11:58 am 
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Location: Annapolis, MD
I'm skeptical....

For starters, if all those IF cans are really 455KHz, it's pretty hard to imagine how they would be used. OTOH, it's quite easy to imagine a builder working just a bit beyond their level of basic understanding. Right here on the forum, we've seen more than one person put a huge effort into "improving" something without having the basic knowledge of the basic principles of operation. Even people that are quite competent sometimes have an over-active imagination.

I would make the schematic first. Without seeing that, I'm in the "curmudgeon camp" that sees a nice assortment of useful parts.

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-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Oct Tue 17, 2017 4:42 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17975
Location: Warner Robins, GA
The quality of work to me looks like whoever built it knew what they were doing so just continue with the recap and when done fire it up and see what you get.


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Nov Wed 01, 2017 10:07 pm 
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Posts: 7469
Location: Beaver Falls, PA. USA
My guess is that it has three separate IF strips; one each for narrow, sharp, and wide. That would explain all the tubes and transformers. I'd also like to see the schematic.

+1 for leaving it in one piece!

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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Nov Wed 01, 2017 10:22 pm 
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Posts: 17975
Location: Warner Robins, GA
Tim Tress wrote:
My guess is that it has three separate IF strips; one each for narrow, sharp, and wide. That would explain all the tubes and transformers. I'd also like to see the schematic.

+1 for leaving it in one piece!


Makes sense as each IF strip can be optimised to its individual sharp narrow and wide functions.


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Nov Fri 03, 2017 10:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 885
Location: St. Louis, MO, USA
Another place to look for information would be electronics magazines like radio news or radio electronics from the 1950s or 1960s. I seem to remember articles about building complex equipment like this from time to time.

Dennis


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 Post subject: Re: Help ID this 3 chassis 19 tube homebrew MONSTER..
PostPosted: Nov Sun 05, 2017 6:09 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 827
Location: Champaign IL 61822
I'm 100.000% sure you can find someone to sell those chassis to :wink: !
If they are interesting, for the right price.

As a clue, what do the two labels by the left two 6H6s say?

I could read the label on that one output transformer ... its a regular 912-C
IF output stage one ... I was looking for push-pull output, but no.

What are the labels on the others? They all look like Miller 912-A,B,C,D
ones like the known one. That's also a big clue .. A is input IF stage,
B is interstage, C and D are output stages.

As to an IF system with that many cans ... I own two commercial boatanchors with
that many ... NC-400 and RA17C12, and they are all quite useful. One can get
a really nice steep skirt IF at 455kHz with that many cans. (If the thing
remains stable).

Before using the magic screwdriver on the cans, try very loosely coupling
(radio off) a good accurate (with digital frequency meter) signal generator
and meter (also loosely) to each can and measure the frequency.

Is there a crystal hidden somewhere?


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