[TTech]

The closest match I can locate as a replacement power transformer is an exact match except for the centered tapped winding to the rectifier
plates. The schematic indicates 250 v. The new one when center tapped would be 275 v. Most tolerances for components in these old radios is +/- 20%  what about voltage, would 275 v work ok ?

Thanks

Tim

[Radioroslyn]

Your good. Wouldn't loose any sleep over a few volts [Image: https://philcoradio.com/phorum/images/sm..._smile.gif]

[RodB]

I would use that transformer then increase R26 to maybe 1500 ohms each to get the correct B+. To get the 6V6 plate voltage down you may have to add a small resistor around 100 ohms between the ot primary and B+. Remember, these voltages were probably taken with older test equipment and with 115-117 volts on the primary so you would probably have to make adjustments even if you had an exact replacement transformer

[TTech]

270DX transformer on order. Thanks guys, think I'll install it, then bring it up on a dim bulb tester with variac  so I can see where my starting point is. Appreciate the quick replies.

Tim

[TTech]

Little update. Installed new power transformer and noticed when input from variac was at household voltage of 120 volts, voltage at primary was only 90 volts.
secondary to rectifier plates only 364 volts instead of expected 550 volts across the secondary winding. Eventually started removing tubes one at a time and with each removed tube things looked better. With 6 of the 9 tubes removed finally started to see things looking normal. 115 volts at primary and 552 volts across the secondary rectifier plate winding.  So with all the original caps still in place will start the process of cap replacements. Was hoping for at least a little life from the speaker but as of yet, silence.

[David]

Please replace all the paper caps before powering up the set. What ever is drawing down the voltage might be what killed the old power transformer.

[TTech]

Yep sure your right. Variac plus dim bulb tester used together as precaution. What would be your guess on normal current draw. Ran it for about 30 sec at full 120 v input to check voltages. At that time it held a steady .2 amp draw. Not trying to abuse anything, still in tube type learning curve.

[TTech]

Little update plus questions. Completed replacement of paper caps. While checking for shorted caps before replacement found one that was shorted. Now the secondary center tapped windings that are high voltage to the rectifier plates is in the normal range for this transformer of 265 volts on either side of the center tap. Decided I would delay increasing resistor values to lower this voltage till I have solved other issues, leaving radio plugged into dim bulb tester and variac.

Secondary winding for 5 volts indicating 5.65 volts. Think I'm happy with this for now.

This radio is the first in my limited experience with tube type radios to have capacitors in 6 of the nine tubes, heater circuits. Secondary winding providing 6.3 volts to the heater circuits, was producing only 3.5 volts. Seems all six capacitors for these 6 tubes shorted to ground. Just clipped one lead on each of the 6 caps and now indicate 5volts on the heater winding instead of 3.5 volts but still low. Now 7 of the 9 tubes exhibit a normal looking glow, two are still dark.

This is also my first tube type radio to have the 12AT7 fm osc converter, 6AU6 fm rf amp, 6BE6 am osc converter, with all associated components enclosed within it's own removable metal cage. Now for my questions.

1. Are the small capacitors in each of the 6 tubes heater circuits and the metal cage to minimize hum or interference in the final stages?

Three of the small capacitors in the heater circuit are of the circular flat mica type. Three are of ceramic tubular type. The three ceramic caps are in the heater circuits of the 6BE6, 6AU6, and 12AT7 tubes which are all enclosed under the removable sheet metal cage.

2. Why were circular flat mica caps used on the three tubes outside the sheet metal cage, and ceramic tubular type used on the heater circuit on the tubes enclosed within the sheet metal cage 

3. What would be my best choice in the replacement of these caps? 


I have tried researching my questions but failed any progress.

Speaker still silent. 


Thanks

Tim

[RodB]

1. Probably to reduce interference mostly when using FM.
2. More stable to temperature changes.
3. You probably don't have to change any of these unless there is an issue. They rarely fail and when it happens it's usually physical. You can probably use NP0 ceramic caps to replace them.
4. Stay out of the FM box as much as possible.

[TTech]

Thanks RodB, will catch myself up on that type of capacitor.

Since I now have power supply voltages that are normal enough to create some kind of sound. Thought I'd investigate why my speaker remains absolutely silent.
Injected an audio tone on the plate of the power tube 6V6GT. Nice clear tone on speaker. Then injected audio tone on the grid of the power tube. Dead, no output. Verified correct voltages on tube socket, looked good enough to me. Removed tube from socket, it looked good, then I shook it. Aha... sounded like a tinkly little rattle. Think I found the grids. New tube on order. Since I've had the chassis out of the cabinet for about a month forgot the radio had been dropped in it's past. Left front corner broken out of place. This could explain my rattling power tube and possibly others. Wish I had remembered that and checked the rest before I ordered just one tube.

[TTech]

Replaced the Power Transformer due to an open center tapped secondary winding. Replaced the output transformer due to the primary winding being open. Replaced all paper caps and still not the very least of sound from the speaker. Received the new 6V6GT output tube in the mail today. Installed it, turned on the power and.... I HAVE NOISE!! I don't know if folks who can't repair or fix anything achieve the same wave of success and satisfaction from the most basic and minimal measurement of success. But, for a person like me it is a true sense of joy.  Applied an audio tone to the grid of newly installed tube. Instead of silence I was rewarded by a nice, not strong, rather a healthy tone from the speaker. Still much to find and replace. No response, just noise on AM but did tune in a very weak FM station.  So by my standard it is no longer a mantle piece decoration as it had been for decades. It's once again a radio.

[David]

Try cleaning the AM FM Phono switch very carefully and check the solder joints for all wire connections go easy on the heat if you have to solder any connections. Did you replace C25,C26 ? Good Luck David

[TTech]

Did not replace C25 or C26. They are part of the circuitry under the sheet metal cover. That area is tightly packed with components some double stacked. A resistor laying on top of a ceramic cap. I'll locate them, hopefully they won't be the components on the bottom of a stack. Not sure I understand the function of C25 and C26 or what the symptom of their various failures could be. Could you help me out on that David? Also need to take the cover off the tuning cap and see what it looks like in there. Another candidate for careful cleaning.

Thanks

Tim

[RodB]

Hi Tim - I'm looking at a Beitmans schematic and can't find C25. C26 is the first cap off the FM terminals on my schematic. That cap is often found on the back of the FM terminal board. I'm thinking you can get FM working by doing a touch up on the FM alignment.

[TTech]

Hey RodB, Per the schematic David was kind enough to supply me on page 1, which is a match to this chassis. C25 and 26 are together in the schematic and part of the AM,FM, Phono selector switch circuit. Agree a general tune up is needed but I also have a lot  of noise even on FM. Next replacement is the power supply electrolytic caps. They tested neither open or shorted so I left them alone till I got some life to the speaker. Also since I remembered this radio had been dropped at one time, guessing a few more new tubes may be in my future. Still have two tubes that remain dark even though they have filament voltage. One in the FM section the other in the AM section.