I have nice little Trav-Ler 5028a AC/DC radio from
about 1947. I just started to restore it and I have
gone through and replaced most of the caps.
The problem I have with the set is that it oscillates -
makes a loud feedback sound - and I can't seem
to find out why. I suspect the problem is coming from
the first stage, which is a 1R5 tube.

If you have any ideas, service notes or even
a schematic, please let me know.

Randall

rbashta@compuserve.com
Randall_Bashta@Stratus.com

:
: I have nice little Trav-Ler 5028a AC/DC radio from
: about 1947. I just started to restore it and I have
: gone through and replaced most of the caps.
: The problem I have with the set is that it oscillates -
: makes a loud feedback sound - and I can't seem
: to find out why. I suspect the problem is coming from
: the first stage, which is a 1R5 tube.

: If you have any ideas, service notes or even
: a schematic, please let me know.

: Randall

: rbashta@compuserve.com
: Randall_Bashta@Stratus.com

Is it a microphonic?...(Physical tube vibration from the speaker) That tends to match a certain freqency in the audio and grow louder and louder as it revibrates itself. if that is it, it will stop with decreased volume..Try another tube..
Also i have one that has a problem at one spot in the volume pot that makes a whistling sound. I think it may be leaking to the body of the pot (as this only happens at one spot..you may want to bypass yours or tack a new one across..
does it make this noise constantly? check insulated wires for grounding to the chassis..
Try searching for shorted caps in the audio with the continuity alarm of your multimeter.

you may have audio leakage somewhere...

: :
: : I have nice little Trav-Ler 5028a AC/DC radio from
: : about 1947. I just started to restore it and I have
: : gone through and replaced most of the caps.
: : The problem I have with the set is that it oscillates -
: : makes a loud feedback sound - and I can't seem
: : to find out why. I suspect the problem is coming from
: : the first stage, which is a 1R5 tube.

: : If you have any ideas, service notes or even
: : a schematic, please let me know.

: : Randall

: : rbashta@compuserve.com
: : Randall_Bashta@Stratus.com
:
: Is it a microphonic?...(Physical tube vibration from the speaker) That tends to match a certain freqency in the audio and grow louder and louder as it revibrates itself. if that is it, it will stop with decreased volume..Try another tube..
: Also i have one that has a problem at one spot in the volume pot that makes a whistling sound. I think it may be leaking to the body of the pot (as this only happens at one spot..you may want to bypass yours or tack a new one across..
: does it make this noise constantly? check insulated wires for grounding to the chassis..
: Try searching for shorted caps in the audio with the continuity alarm of your multimeter.

: you may have audio leakage somewhere...

Thanks for your input. The noise does increase
as the volume pot is turned up. I have ohmed
out all the caps. I have not replaced the caps
which read in the pico farad range, only the
electrolytics and the wax covered ones.

Also, I can barely pick up any stattions. They are
weak and distorted. I have changed the IR5
and I have checked the other ones with a tube
checker.

Anyother ideas.

Thanks

:
: : :
: : : I have nice little Trav-Ler 5028a AC/DC radio from
: : : about 1947. I just started to restore it and I have
: : : gone through and replaced most of the caps.
: : : The problem I have with the set is that it oscillates -
: : : makes a loud feedback sound - and I can't seem
: : : to find out why. I suspect the problem is coming from
: : : the first stage, which is a 1R5 tube.

: : : If you have any ideas, service notes or even
: : : a schematic, please let me know.

: : : Randall

: : : rbashta@compuserve.com
: : : Randall_Bashta@Stratus.com
: :
: : Is it a microphonic?...(Physical tube vibration from the speaker) That tends to match a certain freqency in the audio and grow louder and louder as it revibrates itself. if that is it, it will stop with decreased volume..Try another tube..
: : Also i have one that has a problem at one spot in the volume pot that makes a whistling sound. I think it may be leaking to the body of the pot (as this only happens at one spot..you may want to bypass yours or tack a new one across..
: : does it make this noise constantly? check insulated wires for grounding to the chassis..
: : Try searching for shorted caps in the audio with the continuity alarm of your multimeter.

: : you may have audio leakage somewhere...

: Thanks for your input. The noise does increase
: as the volume pot is turned up. I have ohmed
: out all the caps. I have not replaced the caps
: which read in the pico farad range, only the
: electrolytics and the wax covered ones.

: Also, I can barely pick up any stattions. They are
: weak and distorted. I have changed the IR5
: and I have checked the other ones with a tube
: checker.

: Anyother ideas.

: Thanks

Hi Dave & Randall

Agree with Dave, it's either a microphonic tube or open capacitor causing oscillation. The microphonic tube would be 1S5. It's the 1st audio amplifier. You should be able to tap this tube with a pencil and hear all kinds of ringing if this is a problem. A tube tester will not catch the problem.

An open cap can cause oscillation. Be sure C8, 40 mfd, is good.

Norm

:
: : :
: : : I have nice little Trav-Ler 5028a AC/DC radio from
: : : about 1947. I just started to restore it and I have
: : : gone through and replaced most of the caps.
: : : The problem I have with the set is that it oscillates -
: : : makes a loud feedback sound - and I can't seem
: : : to find out why. I suspect the problem is coming from
: : : the first stage, which is a 1R5 tube.

: : : If you have any ideas, service notes or even
: : : a schematic, please let me know.

: : : Randall

: : : rbashta@compuserve.com
: : : Randall_Bashta@Stratus.com
: :
: : Is it a microphonic?...(Physical tube vibration from the speaker) That tends to match a certain freqency in the audio and grow louder and louder as it revibrates itself. if that is it, it will stop with decreased volume..Try another tube..
: : Also i have one that has a problem at one spot in the volume pot that makes a whistling sound. I think it may be leaking to the body of the pot (as this only happens at one spot..you may want to bypass yours or tack a new one across..
: : does it make this noise constantly? check insulated wires for grounding to the chassis..
: : Try searching for shorted caps in the audio with the continuity alarm of your multimeter.

: : you may have audio leakage somewhere...

: Thanks for your input. The noise does increase
: as the volume pot is turned up. I have ohmed
: out all the caps. I have not replaced the caps
: which read in the pico farad range, only the
: electrolytics and the wax covered ones.

: Also, I can barely pick up any stattions. They are
: weak and distorted. I have changed the IR5
: and I have checked the other ones with a tube
: checker.

: Anyother ideas.

: Thanks

Thanks everyone for your help. I found the problem.
I got the radio off of EBAY as is. When I got it, I
noticed someone had been in it and replaced an
electrolytic capacitor. What I didn't know is that they
removed completely the 3 in 1 caps and removed
all connections. There wasn't any clue that their had
to be other caps involved. I finally found someone
with a Riders which had a prinnt of that model.
I found what values were needed and where they
were to be connected. Now all is well.
I thank every one with their tips and help. They were
all good.