A friend has an Atwater Kent 70 "model L" with a bad power transformer. It has one HV leg starting to fry, with unbalanced output of 422 / 354 VAC. I see that a larger transformer would jam the tuning capacitor's travel. Any suggestions on a replacement of suitable size?
(Outputs are 2.5v @ 12A, 5V @ 2A, and about 425-0-425V for about 80 or 90mA)
Thank You,
Eddie

Are you measuring those voltages open circuit?

:Are you measuring those voltages open circuit?
:
No Doug - the open circuit output is 449 and 379 VAC - and the transformer gets a little warmer than I expected after 10 minutes driving only the filaments. With recitifier installed under normal load, it's 422 and 354 VAC, and the radio will play. The owner said they noticed it started smoking and they unplugged it, and there is quite a bit of wax under it. I told them they might be able to play it up to 10 minutes at a time without damaging anything else (except for further transformer deterioration).
Eddie

Hi Eddie

Transformer is bad for sure with unbalanced HV.

Might try here:

http://www.oldradioparts.com/2a23efl.txt

Transformers with low voltage filaments are near the bottom. If you don't see what you want send Gary an email.

AK55 and AK60 are similar. Should be able to use a transformer from one of them. A standard transformer would need to be under the original box to look right.

Norm

::Are you measuring those voltages open circuit?
::
:No Doug - the open circuit output is 449 and 379 VAC - and the transformer gets a little warmer than I expected after 10 minutes driving only the filaments. With recitifier installed under normal load, it's 422 and 354 VAC, and the radio will play. The owner said they noticed it started smoking and they unplugged it, and there is quite a bit of wax under it. I told them they might be able to play it up to 10 minutes at a time without damaging anything else (except for further transformer deterioration).
:Eddie
:

I'm thinking that a turn might be shorted?

You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm

Also, separate filament and plate xfmrs might provide more mounting flexibility.

I went through this same issue with my AK-70. Because of the way the original transformer is constructed, I was able to rewind the just HV winding. It took a lot of time to set up, but worked well. I had the same concerns about limited space to install a replacement PT.

:I'm thinking that a turn might be shorted?
:
:You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
:
:Also, separate filament and plate xfmrs might provide more mounting flexibility.
:

:I went through this same issue with my AK-70. Because of the way the original transformer is constructed, I was able to rewind the just HV winding. It took a lot of time to set up, but worked well. I had the same concerns about limited space to install a replacement PT.
:
::I'm thinking that a turn might be shorted?
::
::You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
::
::Also, separate filament and plate xfmrs might provide more mounting flexibility.
::
:
:
Radiodaze has the new Hammond RDX-200 general replacement that should work, but with lower HV (350 per leg instead of 425). Has anyone tried to cobble it onto the AK 70 chassis so it won't jam the tuning capacitor? If so, I might order that one.
Thanks for the replies - and I'll probably keep the old transformer in case I can rewind it when I have more time.
Eddie

::I went through this same issue with my AK-70. Because of the way the original transformer is constructed, I was able to rewind the just HV winding. It took a lot of time to set up, but worked well. I had the same concerns about limited space to install a replacement PT.
::
:::I'm thinking that a turn might be shorted?
:::
:::You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
:::
:::Also, separate filament and plate xfmrs might provide more mounting flexibility.
:::
::
::
:Radiodaze has the new Hammond RDX-200 general replacement that should work, but with lower HV (350 per leg instead of 425). Has anyone tried to cobble it onto the AK 70 chassis so it won't jam the tuning capacitor? If so, I might order that one.
:Thanks for the replies - and I'll probably keep the old transformer in case I can rewind it when I have more time.
:Eddie
:
:
:
Who has experience rewinding these? Is the HV winding usually the outermost winding? Is it completely unreasonable to try to reach the bad spot without taking the core apart? How much to professional rewinders charge?
Eddie

Eddie,
I rewound a smaller power xformer for a Heathkit BC-1 AM tuner, and is not for the faint of heart. As I recall HV secondary (2700 turns #38)was the inner winding, primary (750 turns)next, with outer being the filament windings. I had experimented (successfully) with an electro-mechanical coil winder for lattice wound IF xformers, so converted it to be used on larger cores of power xformer. The biggest problem is keeping the turns tight enough without breaking (#38) First try wouldn't fit the window of EI core laminations, but second attempt was successful, and works fine in the assembled unit. I'm not at all fond of this chore, but with no choice, I did it. Have a few sketches. and if interested contact my email.

marv

:::I went through this same issue with my AK-70. Because of the way the original transformer is constructed, I was able to rewind the just HV winding. It took a lot of time to set up, but worked well. I had the same concerns about limited space to install a replacement PT.
:::
::::I'm thinking that a turn might be shorted?
::::
::::You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
::::
::::Also, separate filament and plate xfmrs might provide more mounting flexibility.
::::
:::
:::
::Radiodaze has the new Hammond RDX-200 general replacement that should work, but with lower HV (350 per leg instead of 425). Has anyone tried to cobble it onto the AK 70 chassis so it won't jam the tuning capacitor? If so, I might order that one.
::Thanks for the replies - and I'll probably keep the old transformer in case I can rewind it when I have more time.
::Eddie
::
::
::
:Who has experience rewinding these? Is the HV winding usually the outermost winding? Is it completely unreasonable to try to reach the bad spot without taking the core apart? How much to professional rewinders charge?
:Eddie
:
:

I believe Marv built a rewinding machine that he has used.

Eddie, I suspect the lower HV winding voltage will be OK. If not, you could tinker with the voltage dividers, etc., to boost it up to what the plate voltages are shown as.

Check the value of all the carbon resistors, particulary in the power supply section - they will likely have crept up quite a bit in value, throwing off the volages. This should be a nice set - with two AF stages, the final being a pair of 2A3s in push pull.

Be careful using a pair of 2A3... They draw twice the filament current as 45's which belong in this radio.

Still think you can find a junk chassis of 55,60 or 70 for less than rebuilding a power transformer.

Norm

I believe Marv built a rewinding machine that he has used.
:
:Eddie, I suspect the lower HV winding voltage will be OK. If not, you could tinker with the voltage dividers, etc., to boost it up to what the plate voltages are shown as.
:
:Check the value of all the carbon resistors, particulary in the power supply section - they will likely have crept up quite a bit in value, throwing off the volages. This should be a nice set - with two AF stages, the final being a pair of 2A3s in push pull.
:

Thanks, Norm! I carelessly looked at the schematic for the L-1 chassis - one of the final audio tubes is labeled 2Ab, which I mistakenly read as 2A3. (2A = second audio.)

Eddie, if this radio has a pair of good 45s, your friend is sitting on a small goldmine, particularly if they are the old balloon tubes. It's a shame to say this, but such radios often sell for less than the value of the tubes. And, as far as I know, nobody is making new, erstatz 45s.

:Thanks, Norm! I carelessly looked at the schematic for the L-1 chassis - one of the final audio tubes is labeled 2Ab, which I mistakenly read as 2A3. (2A = second audio.)
:
:Eddie, if this radio has a pair of good 45s, your friend is sitting on a small goldmine, particularly if they are the old balloon tubes. It's a shame to say this, but such radios often sell for less than the value of the tubes. And, as far as I know, nobody is making new, erstatz 45s.
:

::Thanks, Norm! I carelessly looked at the schematic for the L-1 chassis - one of the final audio tubes is labeled 2Ab, which I mistakenly read as 2A3. (2A = second audio.)
::
::Eddie, if this radio has a pair of good 45s, your friend is sitting on a small goldmine, particularly if they are the old balloon tubes. It's a shame to say this, but such radios often sell for less than the value of the tubes. And, as far as I know, nobody is making new, erstatz 45s.
::
:
:
Thanks guys. I'm certainly aware of what people sell #45's for. Fortunately, her #45's are both good - and all her tubes are 'ST bulbs - not nearly as old as the radio. By coincidence, I have the same AK 70 - L1 that I got at an auction - only the cabinet is different. I haven't tested its tubes yet - but those #45's are also 'ST's. I looked yesterday and it also seems to have a bad power transformer - so I am trying to find 2 transformers, and am strongly considering the new Hammond RDX-200, in spite of a growing reputation that they run alarmingly warm when used at full rated output. I hope I can find a way to mount it easily so it won't jam the tuning capacitor.
Eddie

Eddie

Pull the 80 tube and see if transformers get hot? Not impossible but unusual to have two bad power transformers.

Caps in these radios are sealed but sometimes leaky loading down the supply.

Norm

:::Thanks, Norm! I carelessly looked at the schematic for the L-1 chassis - one of the final audio tubes is labeled 2Ab, which I mistakenly read as 2A3. (2A = second audio.)
:::
:::Eddie, if this radio has a pair of good 45s, your friend is sitting on a small goldmine, particularly if they are the old balloon tubes. It's a shame to say this, but such radios often sell for less than the value of the tubes. And, as far as I know, nobody is making new, erstatz 45s.
:::
::
::
:Thanks guys. I'm certainly aware of what people sell #45's for. Fortunately, her #45's are both good - and all her tubes are 'ST bulbs - not nearly as old as the radio. By coincidence, I have the same AK 70 - L1 that I got at an auction - only the cabinet is different. I haven't tested its tubes yet - but those #45's are also 'ST's. I looked yesterday and it also seems to have a bad power transformer - so I am trying to find 2 transformers, and am strongly considering the new Hammond RDX-200, in spite of a growing reputation that they run alarmingly warm when used at full rated output. I hope I can find a way to mount it easily so it won't jam the tuning capacitor.
:Eddie
:

:Eddie
:
: Pull the 80 tube and see if transformers get hot? Not impossible but unusual to have two bad power transformers.
:
: Caps in these radios are sealed but sometimes leaky loading down the supply.
:
:Norm
:
::::Thanks, Norm! I carelessly looked at the schematic for the L-1 chassis - one of the final audio tubes is labeled 2Ab, which I mistakenly read as 2A3. (2A = second audio.)
::::
::::Eddie, if this radio has a pair of good 45s, your friend is sitting on a small goldmine, particularly if they are the old balloon tubes. It's a shame to say this, but such radios often sell for less than the value of the tubes. And, as far as I know, nobody is making new, erstatz 45s.
::::
:::
:::
::Thanks guys. I'm certainly aware of what people sell #45's for. Fortunately, her #45's are both good - and all her tubes are 'ST bulbs - not nearly as old as the radio. By coincidence, I have the same AK 70 - L1 that I got at an auction - only the cabinet is different. I haven't tested its tubes yet - but those #45's are also 'ST's. I looked yesterday and it also seems to have a bad power transformer - so I am trying to find 2 transformers, and am strongly considering the new Hammond RDX-200, in spite of a growing reputation that they run alarmingly warm when used at full rated output. I hope I can find a way to mount it easily so it won't jam the tuning capacitor.
::Eddie
::
:
:
That sounds like a good idea. I only glanced at mine in storage and noticed a blackened smudge around the chassis around the power transformer. I discovered the fuse under the chassis was blown - and couldn't take time to get inside it that day. I picked up on the internet that early AK transformers do go out frequently - - - is that an overblown reputation?
Eddie

:::I went through this same issue with my AK-70. Because of the way the original transformer is constructed, I was able to rewind the just HV winding. It took a lot of time to set up, but worked well. I had the same concerns about limited space to install a replacement PT.
:::
::::I'm thinking that a turn might be shorted?
::::
::::You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
::::
::::Also, separate filament and plate xfmrs might provide more mounting flexibility.
::::
:::
:::
::Radiodaze has the new Hammond RDX-200 general replacement that should work, but with lower HV (350 per leg instead of 425). Has anyone tried to cobble it onto the AK 70 chassis so it won't jam the tuning capacitor? If so, I might order that one.
::Thanks for the replies - and I'll probably keep the old transformer in case I can rewind it when I have more time.
::Eddie
::
::
::
:Who has experience rewinding these? Is the HV winding usually the outermost winding? Is it completely unreasonable to try to reach the bad spot without taking the core apart? How much to professional rewinders charge?
:Eddie
:
:
The outermost winding is the HV winding, and its on a separate bobbin that I was able to remove from the rest of the transformer. I would not recommend a repair of the original winding. Super-fine wire plus compromised insulation from age and heat almost guarentees more than one bad spot and damage trying to get it wound back on. I checked with Hoeber Transformer on rewinding, and they said they would not attempt it on the original core. Of the two AK 70s I dealt with, both had the same issue this the HV winding having shorted turns.
I did ultimately rewind the HV winding on mine with an improvised winder using a 3/8" variable speed drill in a vise. Wasn't pretty but it works and has been running cool for about a year now.

Doug - would a transformer from a Koronette fireplace stereo work in the AK?

:I'm thinking that a turn might be shorted?
:
:You could consider an open-frame xfmr, since they might be a bit smaller. Hammond's are here: http://www.hammondmfg.com/5cpwr.htm
:
:Also, separate filament and plate xfmrs might provide more mounting flexibility.
:

:Doug - would a transformer from a Koronette fireplace stereo work in the AK?
:
Ron, you've done it now. Google searches will again point to this forum for "Koronette fireplace/stereo/liquor cabinet" searches. Thanks a lot.

By the way, you knew that those amazing works of art were built behind the Iron Curtain during the cold war. It now turns out that it was all a KGB plot - the fireplaces contained sensitive listening devices, and they were given out to U.S. Embassies around the world. Most of the Google searches are coming from the CIA, who is trying to figure out how to deal with the problem.