1st RF stage ?

[philo]

After not having done any radio repairs in years, I now have five radios
in my workshop.

The first one belongs to a friend so I have begun to look at it.


It's a Lyric Model S-7


Though I have not found a schematic it's a typical 1930's superhet
employing

2 ) 24A

2) 35/51

1) 27


With a type 80 rectifier and 47 audio output.


After I re-capped it I at first thought it needed no other work as it
had decent audio output.

After about five minutes, the volume dropped to near zero.


If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.


This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.


I decided to bring my Hickock 533a tester down from the attic and all
the tubes check OK

Before I go further, just wondering if anyone here has some ideas.

Thanks

[retiredinprescott]

Post by philo
After not having done any radio repairs in years, I now have five radios
in my workshop.
The first one belongs to a friend so I have begun to look at it.
It's a Lyric Model S-7
Though I have not found a schematic it's a typical 1930's superhet
employing
2 ) 24A
2) 35/51
1) 27
With a type 80 rectifier and 47 audio output.
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.
I decided to bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

I would check to see if B+ is dropping after a few minutes. Does this set have it's filter capacitors in a can full of tar? Have they been replaced? If the filter caps are going bad and leaking I have seen this sort of problem
Mark

[philo]

Post by retiredinprescott

Post by philo
After not having done any radio repairs in years, I now have five radios
in my workshop.
The first one belongs to a friend so I have begun to look at it.
It's a Lyric Model S-7
Though I have not found a schematic it's a typical 1930's superhet
employing
2 ) 24A
2) 35/51
1) 27
With a type 80 rectifier and 47 audio output.
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.
I decided to bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

I would check to see if B+ is dropping after a few minutes. Does this set have it's filter capacitors in a can full of tar? Have they been replaced? If the filter caps are going bad and leaking I have seen this sort of problem
Mark

I did replace the filter caps but I guess I better get my meter out and
start taking readings.

Thanks for the link to the schematic, that should help.

Will start working on this tomorrow

[retiredinprescott]

Post by philo
After not having done any radio repairs in years, I now have five radios
in my workshop.
The first one belongs to a friend so I have begun to look at it.
It's a Lyric Model S-7
Though I have not found a schematic it's a typical 1930's superhet
employing
2 ) 24A
2) 35/51
1) 27
With a type 80 rectifier and 47 audio output.
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.
I decided to bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

I believe this link has the Schematic for the Lyric S7 set:
http://www.nostalgiaair.org/pagesbymodel/817/M0028817.pdf
Mark

[JWil]

Post by philo
After not having done any radio repairs in years, I now have five radios
in my workshop.
The first one belongs to a friend so I have begun to look at it.
It's a Lyric Model S-7
Though I have not found a schematic it's a typical 1930's superhet
employing
2 ) 24A
2) 35/51
1) 27
With a type 80 rectifier and 47 audio output.
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.
I decided to  bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

AGC problem? I had a RF tube fade causing a similar problem. Checked it
on two testers, tested OK. Replaced with a known good tube and the radio
worked.

[Peter Wieck]

Post by JWil
AGC problem? I had a RF tube fade causing a similar problem. Checked it
on two testers, tested OK. Replaced with a known good tube and the radio
worked.

AMEN! To this.

I have a couple of tubes I keep as "demonstrators" that I use to let people know that tube-testers are momentary devices as typically used. Leave these demo tubes on the tester for 5 minutes, and they gradually go from Good to Not so Good to Fail (Hickok 539B).

Peter Wieck
Melrose Park, PA

[philo]

Post by Peter Wieck

Post by JWil
AGC problem? I had a RF tube fade causing a similar problem. Checked it
on two testers, tested OK. Replaced with a known good tube and the radio
worked.

AMEN! To this.
I have a couple of tubes I keep as "demonstrators" that I use to let people know that tube-testers are momentary devices as typically used. Leave these demo tubes on the tester for 5 minutes, and they gradually go from Good to Not so Good to Fail (Hickok 539B).
Peter Wieck
Melrose Park, PA

I generally do not use a tube tester but I was trying to determine if I
had a low emission tube.

Looks like that is not the case.

Have tried other tubes but thus far no difference.

Due to the hot weather I did not feel like doing any troubleshooting
today but will eventually dig deeper.

[philo]

<snip>

Post by JWil

Post by philo
If I removed the antenna and placed it on the grid cap of the second
RF stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51
was low emission, but flipping the two tubes around made no difference.
I decided to  bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

AGC problem? I had a RF tube fade causing a similar problem. Checked it
on two testers, tested OK. Replaced with a known good tube and the radio
worked.

Thanks for the reply.

Good point except this radio is from 1931 or so and AFAIK no AGC

[philo]

<snip>

Post by philo
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second RF
stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51 was
low emission, but flipping the two tubes around made no difference.
I decided to  bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

The tuning capacitor is insulated from the chassis by rubber grommets.
One was worn out and the capacitor was simply at least partially shorted
to ground,

Though I major PITA to replace, a shot of RTV in there should do the trick.

The other radios I have are very low priority but may poke around with
at least one of them someday.

[JWil]

Post by philo
<snip>

Post by philo
After I re-capped it I at first thought it needed no other work as it
had decent audio output.
After about five minutes, the volume dropped to near zero.
If I removed the antenna and placed it on the grid cap of the second
RF stage, it works fairly decently.
This left me with the conclusion that the first RF stage tube 35/51
was low emission, but flipping the two tubes around made no difference.
I decided to  bring my Hickock 533a tester down from the attic and all
the tubes check OK
Before I go further, just wondering if anyone here has some ideas.
Thanks

The tuning capacitor is insulated from the chassis by rubber grommets.
One was worn out and the capacitor was simply at least partially shorted
to ground,
Though I major PITA to replace, a shot of RTV in there should do the trick.
The other radios I have are very low priority but may poke around with
at least one of them someday.

Some of those old radios had rubber grommets on the tuning caps but they
long ago rotted away. So you don't know they were ever there in the
first place. The schematic doesn't show the insulated feet of the cap,
so if it wiggles, I put some grommets on. Radios Daze has grommets from
time to time.

[philo]

On 7/16/19 5:58 PM, JWil wrote:
<snip>

Post by JWil

Post by philo
<snip>

Post by philo
After I re-capped it I at first thought it needed no other work as it
had decent

The tuning capacitor is insulated from the chassis by rubber grommets.
One was worn out and the capacitor was simply at least partially
shorted to ground,
Though I major PITA to replace, a shot of RTV in there should do the trick.
The other radios I have are very low priority but may poke around with
at least one of them someday.

Some of those old radios had rubber grommets on the tuning caps but they
long ago rotted away. So you don't know they were ever there in the
first place. The schematic doesn't show the insulated feet of the cap,
so if it wiggles, I put some grommets on. Radios Daze has grommets from
time to time.

I have some plumbing washers that probably would have worked but it
would really have been a major job to replace them.

But speaking of plumbing


Actually did a 2nd repair job today.


I'm the only person in the world who can repair a radio and need a
plumber when I'm done!


The second radio just needed a filter cap replaced and the pilot lamp.

When I went into my small storage area in the basement to get the bulb,
I noticed a small water leak from a shit off valve.

Had it not been for the radio repair it might have been a long time
before I would have noticed.

Minor leak, no major problem.


When I told my wife she got a good laugh...but not when I said it had
nothing to do with a grid-leak circuit.