Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Philco Model 90 (2-45 tubes) volume control question
#1

I've got a two-45 tube model 90 on the bench. The owner had tried to restore the chassis but created a huge mess - instead of restuffing bakelite cap blocks he just added external caps (all wrong value parts) most of which are hanging from tails of wires. I've got this all straightened out at this point.

My question now is regarding the volume control. There are two sections, one passes a variable amount of antenna to the grid of the RF tube, (via coil #2), and the other straddles "F" and "G" points on the power resistor and controls voltage to the cathodes of two of the 24 tubes.

One of my schematics shows one section to be 5k ohms and the other 250 ohms.

It appears that the prior person flipped the wiring between the two sections, F and G are wired to the 5K section (with the wiper grounded which makes no sense) and the antenna is wired to the 250 ohm section. 

Based upon the schematic that I have with resistance values the current arrangement is backwards.

Can anyone confirm this? (The attached picture has some wires disconnected as I was measuring the sections. You can see that there are two pins grounded, which also doesn't match the schematics)

Thanks very much.


Attached Files Image(s)
   
#2

Hi and welcome to the Phorum,

Here's a couple of things that may make it easier to work on.

https://philcoradio.com/library/images/schem/90a.jpg

https://philcoradio.com/library/download...n%2056.pdf

Methinks you are correct that the two sections are switched, the 5k should be controlling the ant section and the 250 ohm section controls the bias on the rf/if tubes.

GL w/your project! I'm working on a early model 70 which uses the same setup.

When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!

Terry
#3

Welcome to the Phorum!
Icon_wave
#4

Welcome Artbev! Looking forward to your posts on your progress. Take care and BE HEALTHY! Gary

"Don't pity the dead, pity the living, above all, those living without love."
Professor Albus Dumbledore
Gary - Westland Michigan
#5

Thanks everyone for the responses to the volume control question. I rewired it to match the schematic. I also cleaned up the bird's nest created by the owner many years ago. He had hollowed out some of the bakelite cap blocks and used them as terminal strips, others cap blocks were removed and new caps wired unsupported in midair, most were the wrong values.

Finally the cabinet was cleeaned up with a refreshed finish and new grille cloth.

The radio works extremely well, the owner's daughter arranged this repair for her now elderly father (the owner) and she is verry happy and excited to give this to dad for Christmas.


Attached Files Image(s)
       
#6

Nice work!
Icon_thumbup Icon_thumbup




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Need to purchase some accessories for restoration of my Old Philco Radio
Here is a list of resources found in our online library that you might find useful. Mike's Gobs of Knobs email addres...klondike98 — 01:46 PM
First Radio restoration
Hi Tubeman, Welcome to the Philco Phorum.  Phamily Phriendly Pfun with Phine Pholks Phull of Philco Phacts. (See a p...MrFixr55 — 12:33 PM
First Radio restoration
You could post in the WANTED ADs section here on the Phorum and see if anyone has an RF generator that they want to sell...klondike98 — 11:55 AM
Zenith H725
Good ideas, thank you Arrange and Rich. I have the adhesive aluminum foil already and can try that immediately. More ...EdHolland — 10:18 AM
Graphics for majestic 1050 dial glass.
Murf; I found this thread on the ARF, the first photo has a pretty good view of the dial glass. Regards ArranArran — 01:12 AM
Zenith H725
hello Ed, how about that speacial tape used for ducting it's like foil or how about thin piece of aluminum roof flash...radiorich — 12:19 AM
Zenith H725
Ed; One material that I have seen, but never tried for this was material for making exhaust gaskets, it's similar to ...Arran — 11:42 PM
Zenith H725
I just remembered, I have some hi temp silicone rubber material which could do the trick. Or a piece of FR4 laminate. Th...EdHolland — 08:39 PM
Zenith H725
The PSU filter cap arrived today (thank you USPS!) so I will work on that later. Meanwhile, I have the dial, speaker...EdHolland — 06:42 PM
Philco 610B oscillator wiring
Thanks Terry. After checking my notes I think I recorded about -10v at the 6A7 G4/control grid. The screen grid (G3 &...Tubester — 05:59 PM

[-]
Who's Online
There are currently 2623 online users. [Complete List]
» 2 Member(s) | 2621 Guest(s)
AvatarAvatar

>