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 Post subject: squealing below 50...works great above 50
PostPosted: Oct Tue 01, 2019 3:39 am 
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Location: SE Iowa 52626
I have an Eveready Model 21 which originally used five #40 tubes and one 112A. Because 40's are very difficult to find and very expensive if one does I am using 201A's in place of the 40's. All of the resistors were waaaaaaaaaaay high so I placed other resistors under them in parallel to get them correct. Okay, now the radio works fine above 50 on the dial but under 50 all I get is squealing. This is with a ground and long antenna.

Any ideas would be appreciated.

Don


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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Tue 01, 2019 4:34 am 
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Location: S. Dartmouth MA 02748-1225 USA
Different tubes, so the neutralizing condensers C2 & C3 will have to be either changed or adjusted.

Need a '01a with an open filament that is not shorting to other elements or place an insulator on one of the filament pins, the tube must not light to set neutralization.

Install in the socket that has the associated C2/C3 on its grid. turn on radio and dial in the lower end where it squeals. It should not be squealing. Adjust value of C2/C3 such that the received radio signal is at minimum and fix that value. Do the same for the next RF stage. That should stop the squealing.

If it still squeals change the values of the B+ bypass caps, double the value, if .5 make 1, if 1 make two mf.

Be sure any shields or other metal covers are in place.

Use only 90 volts, 4-1/2 volts and 6 volts.

All else fails lower the B+ to 67-1/2 at that B the "C" terminals can be jumped.

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Tue 01, 2019 4:42 am 
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Location: SE Iowa 52626
Chas wrote:
Different tubes, so the neutralizing condensers C2 & C3 will have to be either changed or adjusted.

Need a '01a with an open filament that is not shorting to other elements or place an insulator on one of the filament pins, the tube must not light to set neutralization.

Install in the socket that has the associated C2/C3 on its grid. turn on radio and dial in the lower end where it squeals. It should not be squealing. Adjust value of C2/C3 such that the received radio signal is at minimum and fix that value. Do the same for the next RF stage. That should stop the squealing.

If it still squeals change the values of the B+ bypass caps, double the value, if .5 make 1, if 1 make two mf.

Be sure any shields or other metal covers are in place.

Use only 90 volts, 4-1/2 volts and 6 volts.

All else fails lower the B+ to 67-1/2 at that B the "C" terminals can be jumped.


Thanks for the info, it was appreciated. For your information it works a lot better with C+ and C- not connected at all if that tells you anything.

Don


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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Tue 01, 2019 4:05 pm 
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Quote:
Thanks for the info, it was appreciated. For your information it works a lot better with C+ and C- not connected at all if that tells you anything.
Well, it does...

Without the "C" and the circuit left open, the grid of the last audio tube is left to float seek a negative voltage (generated by passing electrons) that is essentially lowering the gain of that stage. The more negative the voltage on the grid, fewer electrons reach the plate.

With the "C" circuit shorted the voltage becomes fixed at a value set by the grid resistor R6 Since the test was shorted and the set howled then I can only conclude that the values chosen for the grid leak resistor(s) is too high.. At least too high for '01a's, may have been correct for 40's using OEM marked values.

I suspect all resistor values are wrong when changing from the high gain 40 to the low gain '01a

Please post the values chosen for the replacement resistors AND coupling caps in the audio stage, include the detector and the supply voltages.

This should help, mark up the schematic as needed...

Attachment:
National Carbon Eveready 21_72.jpg
National Carbon Eveready 21_72.jpg [ 259.43 KiB | Viewed 1556 times ]


Chas

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Wed 02, 2019 3:32 am 
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Location: SE Iowa 52626
Chas wrote:
Quote:
Thanks for the info, it was appreciated. For your information it works a lot better with C+ and C- not connected at all if that tells you anything.
Well, it does...

Without the "C" and the circuit left open, the grid of the last audio tube is left to float seek a negative voltage (generated by passing electrons) that is essentially lowering the gain of that stage. The more negative the voltage on the grid, fewer electrons reach the plate.
With the "C" circuit shorted the voltage becomes fixed at a value set by the grid resistor R6 Since the test was shorted and the set howled then I can only conclude that the values chosen for the grid leak resistor(s) is too high.. At least too high for '01a's, may have been correct for 40's using OEM marked values.
I suspect all resistor values are wrong when changing from the high gain 40 to the low gain '01a
Please post the values chosen for the replacement resistors AND coupling caps in the audio stage, include the detector and the supply voltages.
This should help, mark up the schematic as needed...
Attachment:
National Carbon Eveready 21_72.jpg

Chas


Chas, I have printed out everything that you suggested and will be trying them in the future. I currently have the chassis in the refinished cabinet and all of the wires tagged and out the back of the cabinet thus before I pull everything back out I want to try a few things. First, I will connect to 67.5 volts instead of 90 and jump the "C" terminals and see if that makes a different. Secondly, I just might be able to get my hands on five #40 tubes at our next radio club auction. As I have all of the resistors back to spec. I would like to try some 40 tubes and see what I get. It may be some time but if the above fails I will start on your last suggestions. Again, it might be some time as I will be out of state quite a bit in the near future.

Thanks again,

Don


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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Wed 02, 2019 5:24 am 
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Location: S. Dartmouth MA 02748-1225 USA
I have what I believe is a 21. I have not confirmed the model but it is EverReady, I have had it for 55 years, a shelf queen. It is just a plain box with 40 tubes and a tiny tuning dial window.

In '76 I went to a collector in Bensonhurst NY, Frank Pagano and bought several radio sets and some 40 tubes. I brought my tube tester and discovered even the new 40 tubes in cartons had some gas. I think I bought enough plus spares for the EverReady.

The 40 has a thoriated filament so if someone offers a "cheap" tube with low emission one could take a gamble.

I also believe that burning the tube for a few hours should fix the gas as well as improve the emission. That is a well known 20's era remedy for weak thoriated tubes.

Lots of data here:

http://www.nostalgiaair.org/References/ ... lash08.htm

I recommend finding one of the early tube rejuvenators. Very useful if the 20's sets are used with some regularity.

BTW if your in MA give me a call.

GL

Chas

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Thu 03, 2019 4:51 pm 
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Location: Keystone Heights, FL, USA 32656
As often happens, seeing a discussion of a radio like one that I have inspires me to get it down and get it working. Same thing here, I have a model 20 that works some, resistors all high in value. Like the OP, I put resistors in parallel to get the correct resistances.
For reference, here is a photo of the area:
Attachment:
DSC03853.JPG
DSC03853.JPG [ 305.64 KiB | Viewed 1447 times ]

And a marked-up schematic:
Attachment:
Eveready 20.jpg
Eveready 20.jpg [ 133.63 KiB | Viewed 1390 times ]

My radio has the 40 tubes and a 112A output tube. Voltages are B+135, A+6.3, C- 9.
Like IGot2's radio, it works good above 50 (low frequencies) but begins to get squealing and howling above 50 on the dial. I found that with as you tune lower on the dial (higher frequencies) the right hand volume control must be reduced until the squealing stops, then tune in the station and make tiny adjustments on the volume to get good reception. Very touchy to tune on the higher frequencies and the station must be pretty strong signal. I am talking almost micro adjustments between squealing and reception.

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Last edited by jrehkopf on Oct Fri 04, 2019 8:17 pm, edited 3 times in total.

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Thu 03, 2019 6:15 pm 
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Jeff,

Does it appear the squealing is in the RF?

Are C2 and the two C3's adjustable and what is their value?

What is the value of R1?

I suppose the neutralization is not adjustable, what if it could be made adjustable and of R1 increased and or a second "R1" added to the grid of the 3rd RF tube?

I can't imagine that "two" receivers suffer the same problem. Could it be a high impedance modern "B" supply, adding additional capacitance or replacing a leaky B Bypass may also help...

The grid resistor was a common device to reduce the gain of the RF stage(s) popular with A-K.

Chas

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Thu 03, 2019 6:54 pm 
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Location: Keystone Heights, FL, USA 32656
I modified the schematic to show that the S2s and C3s are all adjustable. What is their value? I don't know. They are some sort of variable wafer-type.
R1 is 50k ohm, drops the plate voltage for the detector to about 46 volts when playing a station.

I am OK with the way it works, at higher frequencies just have to really back off on the volume (controls the 3 rf tube filaments) and then carefully bring it back up. The tubes are not visibly lit at this point.

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Thu 03, 2019 9:46 pm 
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Great Jeff!

So the neutralization can be adjusted :D

Arrgh, the schematic, unless I am totally blind, R1 is the one and only grid "swamping" resistor it is on the grid of the 2nd RF tube. There are two R1's Ha ha...

My bench is, still, a cluttered disaster. I would pull my EverReady down and get the thing going. I have loaned my ARBE-III to ChrisRI.

I wanted to clarify via your radio while IGot2P is away just how it is laid out and some values of components.

Take a look, again, at R1's location on the grid of 2nd RF and its resistance. I think it should be around 200 to 800 ohms...

Thanks for the notations on the schematic.

Knowing the fact that the neutralizers are adjustable is good enough

All the fun stuff we usually do...

Chas

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Thu 03, 2019 11:29 pm 
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Ahhh, I see it now. Will check it tomorrow (R1).

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Fri 04, 2019 8:18 pm 
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I added the value of the grid R1. I can't see it but it measures 110 ohms.

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Fri 04, 2019 9:28 pm 
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jrehkopf wrote:
I added the value of the grid R1. I can't see it but it measures 110 ohms.

Jeff,

For snicks and giggles, change the value upward, of that R1 grid resistor from 110 ohms, in 100 ohm steps and see how that effects reception... A carbon resistor is fine...

Oh, if you haven't seen this:

viewtopic.php?f=2&t=365653

Should prove useful for posting schematics...

Chas

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Fri 04, 2019 11:23 pm 
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Location: Keystone Heights, FL, USA 32656
Would be nice to try different resistances except it is buried under the tuning assembly cover.

I put some video up in a new thread. viewtopic.php?f=1&t=365673

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 Post subject: Re: squealing below 50...works great above 50
PostPosted: Oct Fri 04, 2019 11:53 pm 
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I suspect it is more likely to be neutralization, but that grid resistor would be a second option after insuring that the neutralization is O.K.

Ha,

Same Peerless speaker in my collection too.

I loaned a second Peerless to ChrisRI for his experiments.

Same technique as neutralizing a genuine "Neutrodyne", will need a dummy tube or thin layer of cello tap around one of the filament pins. Tune the neutro-cap for minimum received signal on the stage with the dummy tube.

May, have to do this with the cover over the tuning condenser, dunno...

GL

Chas

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