Tube Radio Forum - The friendliest radio forum on the net!
Would you like to react to this message? Create an account in a few clicks or log in to continue.

TRF volume TOO HIGH!!

Page 1 of 3 1, 2, 3  Next

Go down

TRF volume TOO HIGH!! Empty TRF volume TOO HIGH!!

Post by datsun280 on Mon Jul 30, 2012 7:39 am

For this TRF radio that has the volume control in the antenna circuit…. What could make the lowest volume setting be equivalent to a high volume sound?
http://www.nostalgiaair.org/Resources/554/M0039554.htm

I ran the voltage measurements using 75wt dim bulb because the beginning low volume is so loud. Sounds good using the dim bulb.

All voltages seem reasonably where they should be except that the det plate is proportionately higher than desired.

What could make this beginning (low setting) volume so darn loud?

Thank you in advance for any help you can offer.

datsun280

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Mon Jul 30, 2012 12:48 pm

First, is it that way on all stations, or, just the very local ones? Radisos, especially this kind, tend to have too much volume on the most powerful stations.
If you are close to several stations, this could be a problem, or, maybe you have an open volume control?
I've seen it happen....
Or, even dirty.
Most of these antenna volume controls are wire wound.
If they get dirty, that can cause them not to work, as can ither the wiper no longer making contact, or, one end going open.
Hope this helps.
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Mon Jul 30, 2012 1:17 pm

The old pot was shot, so a new audio taper pot was installed.
High volume on all. It is like the volume for the set is on steroids!

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Mon Jul 30, 2012 3:38 pm

Audio taper carbon pots will not work for this function. It must have no taper, pure varriable resistance. It's working with RF. Not Audio Frequency.
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Mon Jul 30, 2012 4:43 pm

Thats got to be it Bill!

Thank you! I will get a correct pot and toss it in.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Thu Aug 16, 2012 2:35 pm

How's it coming? Any news on it?
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 5:12 am

Hi Bill, Thank you for following up.
Haven't located a pot for the set. With help from others, have tried to connect the vc to the rf circuit using an audio taper pot instead of the original connection in the antenna circuit, but no luck. Still only high volume. Not able to have any control of the volume.


Last edited by datsun280 on Fri Aug 17, 2012 5:35 am; edited 1 time in total

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 5:25 am

I don't really think a carbon control can work there, but, I may be wrong.
Is it too loud on all stations?
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 5:36 am

Wow you are awake... I thought I was the only one up this early.

Yes it is loud on all stations. It's like there is no vc in the set.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 5:46 am

Can you show me the schematic? Got a link to it?
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 5:49 am

http://www.nostalgiaair.org/PagesByModel/554/M0039554.pdf

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 6:02 am

I think you definately need A wirewound control.
Not sure of resistance. If you mis wired it, that could add to your problem.
Also, what lenghth of antenna do you use, and, have you grounded antenna system?

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 6:07 am

Too long an antenna could also do it.
If grounded to earthground, try disconnecting ground wire.
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 6:18 am

After cleaning out the tar boxes, I am not 100% confident that the connections are correct for the replaced caps. I believe they are correct but that is based on what I know so far in my development.
There is one more cap showing in the two cap boxes than is currently installed in the set.
The antenna length is about 15 feet and it is suspended. Not really sure how to do a grounded antenna system to tell you the truth.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 6:27 am

Right now, I'm wondering if you might have antenna control wired wrong. ie vol control.
You may have missed something.....
Which cap do you think you've missed?
Bil Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 6:36 am

I am going thru my notes. brb with response.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 6:48 am

Each of the 1st RF, 2nd RF caps and resistors are present and connected from cathode to ground. The 1st RF screen cap to ground is present.

Those three are located in the box labeled "Four 1/4 mfd. 115418". These three all had a wire leading to their respective pins. So that is 3 of the 4 in that box.

The fourth in that box is currently connected to a tap on the outside of the box. I am not sure that that was how it originally was inside the tar but I connected it there anyway because there was a remnant of a wire connected inside coming from this tap. This tap is currently not connected to anything.

Have to verify something in the set. brb with continuation.


Last edited by datsun280 on Fri Aug 17, 2012 6:56 am; edited 1 time in total

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 6:53 am

I have to correct the last post Bill. Sorry.

It is correct now.


Last edited by datsun280 on Fri Aug 17, 2012 7:29 am; edited 1 time in total

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 7:03 am

Prior to the recap, the Det screen circuit was connecting to this tap. Since there is no cap showing on the schematic in the Det screen circuit, I left it disconnected.

The other cap box labeled "1 & 1/4 mfd 115417" has a 1.0 mfd connected from the Det cathode to ground. And, a .25 mfd cap connected to the 2nd RF and Det coils.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 7:10 am

The schematic box labeled "Dual 1/2 mfd" is accounted for by 1st AF det to ground, and, voltage divider to ground.

The main cap of .002 mfd is present also.

It seems, presuming that the connections I did were correct, that the missing cap connection in the schematic box labeled "Four 184 mfd 115418" may have been originally connected to the Det screen to voltage divider circuit.

I think I experimented with the vc having this dead ended cap connected to the Det screen at times with no positive result.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 7:16 am

I had to make the "alternative detector output filter" by using a 10k ohm resistor with two .0005 caps as drawn on the schematic. The original coil filter was damaged from removal. I think the .0005 value is what the schematic states but it is hard to read.

The ends of this output filter are in series with the Det plate and 1 AF grid, with the .0005 caps going to ground as shown on the schematic.


datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 7:28 am

The 224's, tuner, electrolytic cap can are all shielded. There is a metal base plate for the underside of the chassis also. It is put back in place each time I have tested a vc repair change.

The two new electrolytics are housed inside the top of the cap can above the chassis. They are inside a thick steel dome cover on top of the large aluminum cap can. The dome cover is a thicker gauge steel than the aluminum cap can. I don't know if the el caps being in this dome cover can contribute to reception seeming to bypass the antenna circuit or not.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 7:36 am

Maybe the voltages would give a clue?:
(using 75 wt dim bulb-otherwise the volume is too loud)

HV = 155v & 149v

Plate:
224 121v target 180v
224 121v target 180v
Det 112v target 115v
227 85v target 110v
245 143v target 215v

Cathode:
224 2.7v target 3.2v
224 2.1v target 3.1v
Det 4.2v target 2.5v *
227 6.3v target 8v
245 ?v target 37v

Screen:
224 61v target 75v
224 61v target 75v
Det 21v target 30v *
227
245

* schem states "not true voltage due to drop and draw of meter"

There is no measurable voltage at the grid caps on DC+ or DC -. Seemed that there was deflection of the needle to negative so I checked DC- but zero for that as well.

The resistance is 5 ohms each for all three 224's.

I noticed while checking the voltage that while checking the 2nd RF, it tuned to a different station. While measuring voltage on the 1st RF and the Det, the same station played that was playing when the set had been first turned on.

Also while testing the voltage, I have the dial inbetween stations so I don't have to hear the loud sound... so the station sounds at a low volume during this. But when my hand gets 3 inches from 1st and 2nd RF grid caps, the station tunes in and is very loud again.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by datsun280 on Fri Aug 17, 2012 8:02 am

Some of the voltages are at, or very near, the values they should be without a dim bulb.

datsun280
Member
Member

Number of posts : 30
Registration date : 2012-07-30

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Bill Cahill on Fri Aug 17, 2012 11:58 am

datsun280 wrote:I had to make the "alternative detector output filter" by using a 10k ohm resistor with two .0005 caps as drawn on the schematic. The original coil filter was damaged from removal. I think the .0005 value is what the schematic states but it is hard to read.

The ends of this output filter are in series with the Det plate and 1 AF grid, with the .0005 caps going to ground as shown on the schematic.

And, there lies part of your problem.
Instead of using a resistor, knocking down needed voltage, you need to replace the coil with correct type coil. It's not there for resistance. It's there to keep rf out of rest of radio. I suspect besides your detector not working, that the rf is getting into the power supply, and, amplifier stages.
You are bypassing the detector by letting rf bleed into the rest of the set.
It may not be your only problem, but, it's certainly one of them.
Not sure what mh rating the coil should be, though. Hope you kept old one. Compare it with replacements, and, try to get something as close as you can. And, me, I'm going back to bed.
Bill Cahill

_________________
Please also join us here; www.videokarma.org/index.php
Bill Cahill
Bill Cahill
Admin
Admin

Number of posts : 4419
Age : 69
Registration date : 2008-03-12

Back to top Go down

TRF volume TOO HIGH!! Empty Re: TRF volume TOO HIGH!!

Post by Sponsored content


Sponsored content


Back to top Go down

Page 1 of 3 1, 2, 3  Next

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum