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

Replacing an Output Transformer with tapped secondary
#1

My 40-216 has a defective output transformer. I doubt I'll find a GOOD replacement any time soon (both halves of the primary were open, and the connections are in the middle so I cannot get to them without removing the secondary!) Likely many potential donor chassis out there ALSO have bad transformers.

Anyway, this set, as well as other large Philcos, use a transformer with a tapped secondary. The tap feeds the tone and volume control circuit - I assume some sort of feedback arrangement.

The secondary was good, so I applied about 2 volts from my HP 200A oscillator at 500 hz and determined that the tap is about 10% of the total.

Can I get away with just shunting the secondary with a couple of resistors to provide the 10% tap? For example, 100 ohms in series with 10 ohms. Perhaps they can even be higher such as 1K and 100 ohms. I realize any parallel resistive load will be reflected back into the primary, so the higher the better.

I calculated that the ratio of the replacement transformer should be about 41. So a 110 ohm load will be reflected as 184K in parallel with the output tubes plate resistance. That should not hurt too much. The tube manuals calls for 10K plate to plate load impedance.

Opinions? Will this work? Is there any limit on the values of the shunt resistors?

Thanks!
Dave




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
HiFi (Chifi) tube amp build - but my own design.
Tim, I have some bakelite sockets in my work shop that I can dig up. I believe quite a few are NOS. I will take photo...RodB — 10:03 PM
Philco 610B oscillator wiring
> The cathode as noted is wired directly to the ground side of the heater filament for that tube, not to the #17 and ...Radioroslyn — 08:12 PM
HiFi (Chifi) tube amp build - but my own design.
Tim; I noticed your post a little late, but I would take one of the junk sockets and try to break a chunk out of it wi...Arran — 08:07 PM
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

[-]
Who's Online
There are currently 1652 online users. [Complete List]
» 3 Member(s) | 1649 Guest(s)
AvatarAvatarAvatar

>