Post by trombone on Nov 15, 2022 19:59:13 GMT 12
We,none of us,fix radios in a social vacuum.We always like to know the backstory,where the radio came from,who its owners were and are ; why do they want it fixed. "The Repair Shop"would be a very dull (& short)show if the human stories surrounding the artifacts were left out.So it was with the big chrome plated Ultimate (though rebranded a John Burns "National")Model RA.
Some of you will recall the oscillator saga in a previous post.Thanks to the ideas from several very helpful Forum readers this problem was very satisfactorily resolved .Various capacitors around the oscillator were replaced even though testing o.k.and the set emerged reliable.I gratefully replaced it in its cabinet ,refitted the knobs and brought it inside as our kitchen radio for its soak test.I even emailed the owner - " Mike - success with radio.Will arrange to drop it off to you soon ".The owner in this case was not me.The owner was a workmate.Mike.
Let me employ an electrical metaphor to explain this next idea.Radio fixing credibility with persons located domestically wavers,at times becomes negative. But even negative credibility has never gone below ,say , a notional minus 4 volts .But offering to fix a radio for a work mate and then undertaking same can potentially become a high risk exercise.We don't fix radios in a social vacuum.
And so a new saga begins to unfold.
Asked questions in the kitchen by persons located domestically while the radio is playing it is considered a courtesy, probably a necessity for continuing harmonious relations , to turn the wireless down. Both while the questions are being asked and while one thinks up the answer.
"Have you paid the Vodafone bill?""What are we having for tea?""Is New Easy Off Bam safe in the septic tank?"
It was during these turndowns during questions that the new problem appeared.This radio has audio distortion - not obvious ,but there.This radio was for a bloke at work.
And it wasn't going right.
Knobs off and back onto the bench.
Probably like you I have a variety of short adapter cables to allow me to plug the speaker into the set on the bench while the speaker in its cabinet sits un-regarded on the floor. So it was here.
So - voltages were checked against the schematic. Various grid biases were especially attended to & scrutinized. Valve books were consulted.Friends at our local VRS were quizzed.
When the volume is turned up the set played okay.When down the raspy tone ,like someone on a bad cellphone line ,was there.
The signal tracer,that refreshing paradigm of distortion free clarity, suggested reasonably conclusively that all was good up to the grid of the 6V6. Various 6V6s were installed with no improvement, then thrust into both valve testers in turn. All tested fine. For heavens' sake - go to bed!
This went on for some days,interrupted by the much more fulfilling planting of potatoes,sowing of beans.
But in time I slunk back into the shed. I tested the 6U7 I'd already tested.I was tempted to retest the 6K8. The 6Q7 was replaced twice.Nothing.Perhaps the i.f.s had been peaked too sharply by a previous repairer? A tentative twist of a screwdriver there as well produced no improvement. And besides it only distorts apparently on low volume. Check the volume control - an unusual one with a tap 2/3 of the way along. All correct ,and smooth there - and again - it seems distortion free at the grid of the 6V6 _ after the volume control.
Disconsolate & nursing a cocoa I take to my bed with Rider and Johnson's "Radio Trouble Shooting Guide Book Vol 1" . Herein are tabulated a frighteningly large array of tuning complexities and malaises. Surely here I would find .... No, nothing that fitted. Just before I went to sleep my eye flicked to page 139 in Rider."a. Dirt or other foreign matter between voice coil and pole piece". And so to sleep.
Looking next morning at Mr Rola's finest inside the cabinet I note that the field is attached to the basket with what the Americans call , I think , "gutter bolts ". Galvanised round headed and slotted machine screws with a coarse thread and square nuts. And furthermore one bolt is a different diameter from the others. Not one looks original. There follows what Wilfred Owen called "an ecstasy of fumbling" as I take the speaker from its tinny cabinet to discover _ that the cone had been possibly removed but certainly re centered and then reglued into the basket , probably with araldite.
The leads from the output transformer to the voice coil promptly snipped and reconnected to the bench test speaker. Clarity!Fidelity!Bliss!At both high and low volumes.
Whoever had overhauled this speaker in the past had done a creditable job. It went okay at higher volumes ,presumably with more ergs to overcome the friction between pole piece and voice coil.But at low volume the rasping was there and apparently foretold a continuing and increasing electrical distortion problem.
Subsequently a p.m. speaker has been installed & the field winding replaced with a resistor. Mike has been emailed.The social milieu has been restored and may even trend positive.
Some of you will recall the oscillator saga in a previous post.Thanks to the ideas from several very helpful Forum readers this problem was very satisfactorily resolved .Various capacitors around the oscillator were replaced even though testing o.k.and the set emerged reliable.I gratefully replaced it in its cabinet ,refitted the knobs and brought it inside as our kitchen radio for its soak test.I even emailed the owner - " Mike - success with radio.Will arrange to drop it off to you soon ".The owner in this case was not me.The owner was a workmate.Mike.
Let me employ an electrical metaphor to explain this next idea.Radio fixing credibility with persons located domestically wavers,at times becomes negative. But even negative credibility has never gone below ,say , a notional minus 4 volts .But offering to fix a radio for a work mate and then undertaking same can potentially become a high risk exercise.We don't fix radios in a social vacuum.
And so a new saga begins to unfold.
Asked questions in the kitchen by persons located domestically while the radio is playing it is considered a courtesy, probably a necessity for continuing harmonious relations , to turn the wireless down. Both while the questions are being asked and while one thinks up the answer.
"Have you paid the Vodafone bill?""What are we having for tea?""Is New Easy Off Bam safe in the septic tank?"
It was during these turndowns during questions that the new problem appeared.This radio has audio distortion - not obvious ,but there.This radio was for a bloke at work.
And it wasn't going right.
Knobs off and back onto the bench.
Probably like you I have a variety of short adapter cables to allow me to plug the speaker into the set on the bench while the speaker in its cabinet sits un-regarded on the floor. So it was here.
So - voltages were checked against the schematic. Various grid biases were especially attended to & scrutinized. Valve books were consulted.Friends at our local VRS were quizzed.
When the volume is turned up the set played okay.When down the raspy tone ,like someone on a bad cellphone line ,was there.
The signal tracer,that refreshing paradigm of distortion free clarity, suggested reasonably conclusively that all was good up to the grid of the 6V6. Various 6V6s were installed with no improvement, then thrust into both valve testers in turn. All tested fine. For heavens' sake - go to bed!
This went on for some days,interrupted by the much more fulfilling planting of potatoes,sowing of beans.
But in time I slunk back into the shed. I tested the 6U7 I'd already tested.I was tempted to retest the 6K8. The 6Q7 was replaced twice.Nothing.Perhaps the i.f.s had been peaked too sharply by a previous repairer? A tentative twist of a screwdriver there as well produced no improvement. And besides it only distorts apparently on low volume. Check the volume control - an unusual one with a tap 2/3 of the way along. All correct ,and smooth there - and again - it seems distortion free at the grid of the 6V6 _ after the volume control.
Disconsolate & nursing a cocoa I take to my bed with Rider and Johnson's "Radio Trouble Shooting Guide Book Vol 1" . Herein are tabulated a frighteningly large array of tuning complexities and malaises. Surely here I would find .... No, nothing that fitted. Just before I went to sleep my eye flicked to page 139 in Rider."a. Dirt or other foreign matter between voice coil and pole piece". And so to sleep.
Looking next morning at Mr Rola's finest inside the cabinet I note that the field is attached to the basket with what the Americans call , I think , "gutter bolts ". Galvanised round headed and slotted machine screws with a coarse thread and square nuts. And furthermore one bolt is a different diameter from the others. Not one looks original. There follows what Wilfred Owen called "an ecstasy of fumbling" as I take the speaker from its tinny cabinet to discover _ that the cone had been possibly removed but certainly re centered and then reglued into the basket , probably with araldite.
The leads from the output transformer to the voice coil promptly snipped and reconnected to the bench test speaker. Clarity!Fidelity!Bliss!At both high and low volumes.
Whoever had overhauled this speaker in the past had done a creditable job. It went okay at higher volumes ,presumably with more ergs to overcome the friction between pole piece and voice coil.But at low volume the rasping was there and apparently foretold a continuing and increasing electrical distortion problem.
Subsequently a p.m. speaker has been installed & the field winding replaced with a resistor. Mike has been emailed.The social milieu has been restored and may even trend positive.
