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 Classic 5 valve very low volume.
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 Return to top of page · Post #: 16 · Written at 9:18:07 PM on 14 October 2013.
Marcc's avatar
Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438

A couple of observations: Beware of modern digital meters in Valve sets. Many cannot handle the voltages of them.

What voltage filter caps were used?

Something is wrong with 5Y3 socket, what you say is not as it should be: Check it. You are possibly feeding AC into B+ and the filter caps are likely the rectifier.

The filaments of a 5Y3 are pins 2 & 8 and should not ever be grounded. B+ comes off one of them

The Anodes are 4 & 6 and should have nothing other than the outside of the secondary attached to them. Octal socket, looking at wiring side reads clockwise starting at the spigot (so pin 1 is left of the notch). Only the CT of those windings goes anywhere near earth (chassis)

It is not unusual for the other socket terminals to be used as tags of convenience.

Marc


 

 Return to top of page · Post #: 17 · Written at 11:05:17 PM on 14 October 2013.
GTC's avatar
Location: Sydney, NSW
Member since 28 January 2011
Member #: 823

I didn't bother scouring (2), (3), and (4) for differences when I sent them as I expected that you would be able to marry at least one of them up with the actual chassis that you have in front of you.

In any case, let's use (4) for reference in this discussion.

Firstly I could only find one filament winding on my unit. The voltage reading between these 2 wires going to 5Y3GT is 5.2 volts AC

That's the 5 volt winding.

there is no second feed to supply the other valves with 6.3 volts.

In the schematic, the 6.3 AC volt winding (above the double pole power switch) is shown as having one side earthed to chassis.

The readings I got for Pin 4 and Pin 6 to chassis on 5Y3 was 299 volts AC for each reading.

when I take a reading from terminal 6 which has one of the filament wires attached to chassis I get 299 volts

Pin 6 is one of the anodes which takes AC from the transformer.

The rectified voltage appears at the cathode of the rectifier. In the case of the 5Y3, which is a directly-heated valve, the filament acts as the cathode.

On terminal 8 on 5Y3 the reading was 338 volts DC and the reading for the junction of the choke and the 16micro farad cap was 306 volts.

Okay, so filtered HT is getting out of the power supply. That's good.

6AQ5 pin 5 294 volts DC,
6BD7 Pin 1 60 volts,
6AD8 Pin 6 305 volts,
6AN7 Pin 7 308 volts and for Pin 8 100 Volts.

As you can see the voltages are all over the place.


Assuming that your meter is working correctly on the DC range, and that you've used the correct pins for measurement, the 6BD7 anode voltage looks alarmingly low.

Follow the circuit from the 16μF capacitor and take DC measurements at each of the component junctions on the way to the 6BD7's anode. Try to find where the HT suddenly drops.


 

 Return to top of page · Post #: 18 · Written at 11:13:58 PM on 14 October 2013.
Monochrome625's avatar
Location: Melbourne, VIC
Member since 20 September 2011
Member #: 1009

Those voltages seem way too high. There should be no more than 250 volts on the anodes of all the valves, excepting the rectifier. In fact some of the valves in normal operation will have much less than 250 volts on the anodes.

What about the resistors? Were they checked and replaced as necessary?

These AORSM drawn circuits have a unusual way of showing component values, especially resistors. Resistor values without a decimal point are read in ohms. Those with a decimal point are read in point of a megohm. Those values in the megohms have the decimal point after the value.

Also, I'd replace the 250pf mica that goes between pin 1 of the 6BD7 & chassis. These are notorious for failing and will cause low volume if faulty.

I've sent you a circuit diagram with the valve pin out numbers drawn in. Don't worry if have pin 6 & 8 mixed up on the 6BD7 - they both do the same thing.


 

 Return to top of page · Post #: 19 · Written at 11:16:57 PM on 14 October 2013.
GTC's avatar
Location: Sydney, NSW
Member since 28 January 2011
Member #: 823

I see that Marc has posted while I dawdled in my response. His point about meters is moot. You may be getting quite incorrect readings.

What meter are you using? What is its highest DC range?


 

 Return to top of page · Post #: 20 · Written at 12:15:46 AM on 15 October 2013.
Marcc's avatar
Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438

"The readings I got for Pin 4 and Pin 6 to chassis on 5Y3 was 299 volts AC for each reading.

when I take a reading from terminal 6 which has one of the filament wires attached to chassis I get 299 volts"

Please note: This is a repeated statement NB the comment about pin 6: Pin 6 should not have a filament wire on it. It should only have a secondary AC feed, naught else.

There is little point speculating what is wrong elsewhere until such time as we clarify if wiring of the 5Y3 is correct, which the quote says it isn't.

Marc


 

 Return to top of page · Post #: 21 · Written at 12:50:09 AM on 15 October 2013.
GTC's avatar
Location: Sydney, NSW
Member since 28 January 2011
Member #: 823

when I take a reading from terminal 6 which has one of the filament wires attached to chassis

I'm thinking that '6' is either a typo or a misidentified pin number.

I see that Mono has sent him a schematic with the pin numbers marked on it. That should help clarify the situation.



 

 Return to top of page · Post #: 22 · Written at 9:31:16 PM on 13 January 2014.
AndyRBin's Gravatar
Location: Chuwar, QLD
Member since 12 August 2013
Member #: 1395

Hi GTC I sent a reply in October with the voltage readings.You must have missed it but I was not to concerned as I thought you may have been tied up with the fires.
I can carry on with the checks but have been thinking maybe it would be best to get somebody who knows what they are doing to repair it for me.
Do you know of anybody that I can send to to get it repaired but not at an exorbient price. Any help would be appreciated.

Regards
Andy
P.S. My apologies I found your response as well as others. Will check tomorrow.


 

 Return to top of page · Post #: 23 · Written at 10:42:14 PM on 13 January 2014.
GTC's avatar
Location: Sydney, NSW
Member since 28 January 2011
Member #: 823

I had completely forgotten about this thread. Thankfully those fires didn't reach Sydney. When you didn't respond I figured you'd managed to sort it out yourself based on the various suggestions posted.

As Marcc says above, the need to clarify what's happening with the 5Y3 rectifier wiring is crucial.

As for repairers, I can't immediately think of any QLD people myself, but the QLD branch of the HRSA may be able to suggest some locals. Can't vouch for anybody's pricing either.


 

 Return to top of page · Post #: 24 · Written at 9:05:14 PM on 16 January 2014.
AndyRBin's Gravatar
Location: Chuwar, QLD
Member since 12 August 2013
Member #: 1395

Hi GTC I think I am getting somewhere.
5Y3GT is ok.Pin 6 to chassis 285 volts. Pin 4 to chassis 285 volts and of course Pin 4 to Pin 6 570 volts as you explained. Voltage between pin 8 and pin 2 5.1 volts AC.
Voltage at terminal 8 to chassis (Where the 8 micro farad cap is connected) 329 volts DC.
Voltage at the junction of the choke and 16 micro farad cap 288 volts DC.

From this I assume that the 5Y3GT voltages and connections are ok.

Voltage reading at Pin 5 on 6AQ5 276 volts DC.
Voltage reading at Pin 1 on 6BD7 56 volts DC.
Voltage reading at Pin6 on 6AD8 289 volts DC
Voltage reading at Pin 7 on 6AN7 289 volts DC
and voltage reading on Pin8 on 6AN7 98 volts DC.

Everybody is saying that the voltage on 6BD7 is too low so I disconnected the resistor in this line and connected my resistor calculator and adjusted the voltage from 56 volts to 275 volts and the size of the resistor I required was 1.5K. I did the same on 6AN7.

Somebody mentioned that the 250pf mica can cause low volume so I have decided to replace all pf micas and also all resistors.
But I need help with resistor sizes. I know that a number with no decimal point is in OHMS. I assume that a number followed by a decimal point reads in K's but the rest I don't know.

.1, .04, .044, .05 etc.

6AN7,6AD8,6BD7 and 6AQ5 all have 6.3 volts present.
Although confusing the winding is grounded to chassis on one end the otherside is the 6.3 volt AC feed. Because of this all the valves have at least one pin to chassis.

Regards
Andy


 

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