Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

Hi Mike

Check your speaker. Does the cone move freely without rubbing?

Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.

Norm

:Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

Thanks, Norm. Yes, the speaker is fine. I've tried a couple. Do I make that voltage check by putting the negative probe on the chassis and the positive probe on the tube pin?

:Hi Mike
:
: Check your speaker. Does the cone move freely without rubbing?
:
: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
:
:Norm
:
::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

Mike: Norm is suggesting that you check the grid bias of the output 41 tube. Needs to be negative in relation to the cathode.

Touch the positive voltmeter lead to Pin 4 (the control grid) and the negative lead on Pin 5 (the cathode). You should read a negative voltage.

:Thanks, Norm. Yes, the speaker is fine. I've tried a couple. Do I make that voltage check by putting the negative probe on the chassis and the positive probe on the tube pin?
:
::Hi Mike
::
:: Check your speaker. Does the cone move freely without rubbing?
::
:: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
::
::Norm
::
:::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

Negative lead should go to pin 4, since it's the negative item. The positive lead should go to pin 5, since it's the positive item. Your meter might not give you an accurate voltage depending on how it loads the grid resistor.

T.

Also, with this set having the volume control in the RF section, fuzzy sound is possible at low volumes. Volume is controlled by changing grid-cathode bias, which can cause fuzziness in some RF circuits. Perhaps I can come up with a solution if you are absolutely sure that all components in the radio are functioning properly

T.

Check R55 and see to it that it has not drifted. Try substituting a smaller value (parallel with another resistor of the same value or slightly lower...go lower still if that doesn't correct problems, but stop if it becomes difficult to lower the volume).

Also, if your tube tester has 4, 5, 6, and 7 pin sockets, you can test those tubes. Does your tester give settings for 6A8, 6K7, 6Q7 (or 6SQ7), 6F6, and 5Y3? These tubes are equivilant to the tubes in your radio. 6U7 might be more of an equivilant to the #78, though using settings for either 6U7 or 6K7 will probably give you a rough idea as to where your #78 tube stands. What kind of tester do you have anyway?

Thomas

Well, my tube tester only has the octal sockets and miniature sockets for tubes that are newer. I appreciate all your thoughts.
:Check R55 and see to it that it has not drifted. Try substituting a smaller value (parallel with another resistor of the same value or slightly lower...go lower still if that doesn't correct problems, but stop if it becomes difficult to lower the volume).
:
:Also, if your tube tester has 4, 5, 6, and 7 pin sockets, you can test those tubes. Does your tester give settings for 6A8, 6K7, 6Q7 (or 6SQ7), 6F6, and 5Y3? These tubes are equivilant to the tubes in your radio. 6U7 might be more of an equivilant to the #78, though using settings for either 6U7 or 6K7 will probably give you a rough idea as to where your #78 tube stands. What kind of tester do you have anyway?
:
:Thomas

Thanks for appreciating my thoughts. Did you check R55?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

Yep, that one's OK, but I did find a problem with a resistor value in the 41's grid circuit. A funny colored stripe. Now I've got -17 volts on the grid and a lot better sound. Thanks for your help. Did you check R55?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

Norm, with positive probe on pin 4 and negative probe on pin 5, I get -.5 volts. I'm guessing that indicates a problem either with the tube or the bias voltage. Right?

Hi Mike
:
: Check your speaker. Does the cone move freely without rubbing?
:
: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
:
:Norm
:
::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

:Norm, with positive probe on pin 4 and negative probe on pin 5, I get -.5 volts. I'm guessing that indicates a problem either with the tube or the bias voltage. Right?
:
:Hi Mike
::
:: Check your speaker. Does the cone move freely without rubbing?
::
:: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
::
::Norm
::
:::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.

Mike,

You may want recheck the negative DC voltage on the grid (pin 4) of the 41 and work your way from the grid thru R5, R23 to the junction of R22 and the HV centertap. There should definitely be more than minus 0.5 volts on the grid of the 41. If you unsoldered connections around that area, doublecheck your work. If R5, 23 and 22 were replaced make sure you replaced them with the right value.

Radiodoc

OK, Radiodoc, I checked the voltage again, and -.5 comes up again. If I reverse the probes on the pins(red on 4 and black on 5) I got a +.5 reading. I'll follow through on those resistors.
::
::Hi Mike
:::
::: Check your speaker. Does the cone move freely without rubbing?
:::
::: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
:::
:::Norm
:::
::::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.
:
:Mike,
:
:You may want recheck the negative DC voltage on the grid (pin 4) of the 41 and work your way from the grid thru R5, R23 to the junction of R22 and the HV centertap. There should definitely be more than minus 0.5 volts on the grid of the 41. If you unsoldered connections around that area, doublecheck your work. If R5, 23 and 22 were replaced make sure you replaced them with the right value.
:
:Radiodoc
:

Mike,

Measuring at the junction of the high voltage centertap and resistor R22 ( I believe there is an electrolytic minus connected too) there should be DC voltage considerably higher than minus 0.5 volt. I believe it was mentioned it should be around a minus 15 volts. If you have it there but not on the grid of the 41, then the problem is between the two points, two resistors and a cap to ground.

Radiodoc

:OK, Radiodoc, I checked the voltage again, and -.5 comes up again. If I reverse the probes on the pins(red on 4 and black on 5) I got a +.5 reading. I'll follow through on those resistors.
:::
:::Hi Mike
::::
:::: Check your speaker. Does the cone move freely without rubbing?
::::
:::: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
::::
::::Norm
::::
:::::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.
::
::Mike,
::
::You may want recheck the negative DC voltage on the grid (pin 4) of the 41 and work your way from the grid thru R5, R23 to the junction of R22 and the HV centertap. There should definitely be more than minus 0.5 volts on the grid of the 41. If you unsoldered connections around that area, doublecheck your work. If R5, 23 and 22 were replaced make sure you replaced them with the right value.
::
::Radiodoc
::

Good call, Radiodoc. I did have a bad value at that junction. I misread an odd colored stripe. I now have -17 volts on the grid and much better sound. Thans for your help.
::Norm, with positive probe on pin 4 and negative probe on pin 5, I get -.5 volts. I'm guessing that indicates a problem either with the tube or the bias voltage. Right?
::
::Hi Mike
:::
::: Check your speaker. Does the cone move freely without rubbing?
:::
::: Can you measure voltages? Pin #4 on your 41 tube must be negative in relation to pin #5 by about 15 volts. Not likely a tube but in most cases you can check tube operation by measuring voltages.
:::
:::Norm
:::
::::Folks, I have a followup question regarding the Arvin 518. I've replaced all the capacitors and resistors. The quality of the sound is fuzzy. It clears up quite a bit at louder volume. I'm wondering if a soft tube might be the problem. I don't have a way of testing those older tubes. The line up is 6A7 - oscillator/detector; 78 i.f. amp; 76 second dector; 41 output; 80 rectifier. I'm wondering how likely it is that a bad tube is the problem and which one might be the most likely culprit. Perhaps there's no way of knowing without testing or substituting, but I'd appreciate your thoughts. Another thought I had was a failing potentiometer, but I'm reluctant to touch it because it's so old an unique looking. Thanks.
:
:Mike,
:
:You may want recheck the negative DC voltage on the grid (pin 4) of the 41 and work your way from the grid thru R5, R23 to the junction of R22 and the HV centertap. There should definitely be more than minus 0.5 volts on the grid of the 41. If you unsoldered connections around that area, doublecheck your work. If R5, 23 and 22 were replaced make sure you replaced them with the right value.
:
:Radiodoc
: