[NostalgiaRadioTime]

The good news: I got the 13 tube Silvertone chassis recapped and playing.

The bad news: It has a motorboating issue related to the tone control and the flash tuning mode.

Here is a schematic (my set uses the bottom schematic, with a 6Q7 1st AF tube used instead of the 6R7 shown...Silvertone made some changes to these throughout the model year):

   

I've been working off of the Nostalgia Air schematic at this link on page 2 of the PDF file (again, the version on the bottom of the page, the 4588A matches mine and the yellowing paper schematic attached to the side of my chassis).

http://www.nostalgiaair.org/pagesbymodel...017127.pdf

So there seems to be some kind of a short within the tuning switch or relays, as when the BROAD/SHARP/FLASH tuning knob is turned to FLASH, it just motorboats with stations coming in faintly. In this mode, when you turn the separate tone control, lowering the tone increases the speed of the motorboating. When you turn the tuning control the opposite
direction, the motorboating slows down. Now in the BROAD or SHARP position, the radio plays fine with the tone set to more of a treble position, but when turned down to more bass (about 3/4 of the entire range), the set begins to motorboat (but not as bad as in the FLASH mode).

At one point when I went to flash mode, it killed all sound. Dead silence on all bands. And when it did come back on after turning it off for a few minutes, one of the 6N6's developed an internal short visible within the tube (a pulsating grey streak).

I haven't done a thorough voltage check yet, but voltage does seem to be a bit high. I'm getting 6.8 volts on the 6.3 main dial lamp, and at 120 VAC, the set is drawing .25 amps (which with 13 tubes doesn't seem totally out of line).

So if anyone has restored one of these high tube count 1937 Silvertone consoles with the Flash Tuning and can point me in the right direction as to what could be the culprit, I'd be most grateful. And I'm hoping Terry can give the schematic a scan and see if he can spot anything that could cause this weird issue. I traced out the tone control, the volume control, all the electrolytics and it all checks out per the schematic. Double checked the ground connections and they too seem fine.

[NostalgiaRadioTime]

Swapped out all tubes one by one again, even trying metal tubes where available all to no change. Then I took some voltage readings today.

1.) 5X4 I get 410VAC across pins 3 & 5 (plates), and 358 DC across pins 7 & 8. Schematic calls for 325 V
2.) 6N6's I get 310 on pin 3, and 325 on pin 4. Show be 280 & 290 respectively
3.) 6C5 Phase Changer I get 174 on pin 3 and 8 on pin 8. Should be 165 and 12 respectively
4.) 6C5 2nd AF I get 182 on pin 3 and 8 on pin 8. Should be 155 and 12 respectively
5.) 6Q7 1st AF I get 172 on pin 3. Should be 110
6.) 6J7 AFC I get 214 on pin 3, 111 on pin 4, and 3 on pin 8. Should be 190, 90, and 4.25 respectively
7.) 6C5 OSC I get 81 on pin 3. Should be 90
8.) 6K7 IF I get 283 on pin 3, 84 on pin 4, 1.2 on pin 5 and 7.2 on pin 8. Should be 255, 110, 4.25, 4.25
9.) 6K7 RF I get 281 on pin 3, 83 on pin 4, 1 on pin 5 and 9.7 on pin 8. Should be 255, 110, 7, 7
10.) 6L7 translator I get 281 on pin 3, 84 pin 4, 0 on pin 5, and 9.7 on pin 8. Should be 255, 110, 7, 7

Voltages are running a bit high in general, and none on pin 5's of the 6K7 RF and 6L7 tubes. I can hear the contacts arcing under the chassis when the set is first turned on. The flash tuning light flickers on and off for about 10-15 seconds then it settles down. Need to try to figure out how to get those contacts apart and see why no voltage appears on pin 5.

[NostalgiaRadioTime]

   

Lots of strange things in this circuit, to me anyhow. For one, there was no connection between pin 8 and pin 5 on the 6K7 RF tube as shown above. The set plays the same with or without a wire connected between them.

And I'm not getting any voltage...zero, zip, nada, on pin 5 of the 6L7 and there's supposed to be a small amount, about 7 volts. I replaced the 50 mmf cap, and the 50K resistor and verified they are connected correctly. I get 88 volts on pin 5 of the 6C5 tube below where one end of the 50 mmf cap is connected, yet on the opposite side of the cap, which goes to pin 5 of the 6L7 I get nothing. I wouldn't think a small picofarad cap would kill all of the voltage across it?

[462ron]

Hi Greg, I have no experience with your set but a couple things. Your voltages reading high but to me not exceptionally so but could be due to using a modern high impedance volt meter compared to what was used back in the day, thus not  loading down the circuits as much. On another note, you said your radio draws .25 amps, that’s just 30 watts, that seems low for a 13 tube set! Good luck!

Ron

[captainclock1988]

Hi, I'm wondering if your radio isn't a rebadged Sparton 1068 like the one seen in this thread here that was done by one of our fellow members Buzz.

If so, maybe try taking a look at the Sparton Schematic and see what's what there.

Also my Solid State Pioneer SX-1000 TD does a similar thing to your radio where it wants to motorboat if the Bass and Treble are turned all the way up, but works fine when its set to "flat" setting (where the Bass and Treble Controls are set to the middle) and the weird thing is that with my Pioneer it only does it in the AM Band Setting, all the other Settings work fine, except when it is in the middle of motorboating  and you switch it between the different band and input settings then the radio will continue to motorboat until you turn down the tone controls or turn off the radio and turn it back on again, but with my stereo its definitely tied with the tone controls (which in the Pioneer SX-1000 its the Control Amplifier Stage).

I hope this helps.

-Levi

[NostalgiaRadioTime]

Hi Levi,

I've watched Buzz's videos on the Sparton and, while it's a similar high end, high tube count radio, it is quite a bit different than this Silvertone.

I think I have the motorboating problem solved after fiddling with the flash tuning relay and contacts. I can see why they only used this feature one year. As I've read it was notoriously troublesome even when new.

If you're curious, here is a little demo video of someone else's 4588 showing how the flash tuning works:

https://www.youtube.com/watch?v=EpleHtaBvoo

Thanks for your input!

[captainclock1988]

No Problem, I'm glad I could help, and I'm glad you were able to fix the issue.

[NostalgiaRadioTime]

After nearly 2 solid weeks of work, the 1937 Silvertone model 4588A radio is completed. I finally found the problem with motorboating and erratic sound....but only by using a small LED flashlight and a magnifying glass and looking at each pin on each tube socket. I found a blob of loose solder hiding under one of the pins on the AVC 6C5 tube that was intermittently shorting to ground.

With 13 tubes it is a powerhouse...it plays loud and strong with the volume control barely opened. At half volume it would rattle the windows. I managed to salvage the original finish on the cabinet too! The only refinishing was around the bottom base...badly chipped from decades of vacuum cleaner bangs. This one is a keeper!

   

   

   

   

[RodB]

Beautiful set Greg, you have to be proud of this one.

[Radioroslyn]

Very Nice!!!!

[Eliot Ness]

That is a beauty

[morzh]

A beautiful radio.