HMV 501 Radiogram issues

[ms660]

Just to note there's an error in the Trader sheet version, the voltage drop across R12, either the voltages are wrong or the value of R12 is wrong.

Lawrence.

[PJL]

Originally Posted by ms660

Just to note there's an error in the Trader sheet version, the voltage drop across R12, either the voltages are wrong or the value of R12 is wrong.

Lawrence.

Already noted that in post #14 and it looks like the trader is missing V1 anode feed, R3 and C9, shown on the 'Servicing' sheet available above and that would explain the difference.

The only option here is to go through the entire radio checking against the 'chosen' circuit and adding component values. Whilst doing this the measured values can be checked against the component markings.

Until that is done it will not be possible to tell if the valves are OK.

[ms660]

Originally Posted by PJL

Already noted that in post #14

Yes but not as an error.

The schematics are different in several ways.

Lawrence.

[mancunian69]

Hi,
As I said before, I am using the service manual from Radio Museum.

There are 4 sheets, but if you look at the two marked 435, 501 this is where I am getting component values from. I have noticed that some of the resistors in the set do not tally with the sheet.

Strangely, R14 was missing when I got the set. It is now in place.

I printed out the data sheet for the MS4B tube and will probe that one today and get back.
This is the type that has the anode at the top of the glass bulb. I will try and find a plastic cap for that instead of just a bare metal clip.

Michael

[ms660]

Does your receiver have a variable capacitor reaction control (VC4) ?

Lawrence.

[PJL]

The missing R14 would mean it started off life more like the Trader version but probably with R3 and C9.

Isn't VC4 the aerial trimmer but it is not included in the Radiomuseum parts list and would be C18 in the Trader sheet.

I still feel the circuit and values need to be checked against a 'master' circuit diagram before any more work is done. My preference would be to use the Trader sheet as the reference. The Trader makes reference to 2 parallel 4uF capacitors making up C9.

[mancunian69]

Hi,
Please advise where I can get hold of the trader sheet that you refer to. Maybe it's better, I don't know.

Anyway, voltages at V1 on MW are as follows:

Anode 159v
Screen 20.5v
Cathode 0.2v

Some resistors are of different values to that on my list. See attached. The white resistor is 25kOhm. On my schematic it is listed as 10k (R3)

The bank of resistors in the image I have checked in circuit and they all check out.

With the set off and in gram mode, the resistance of the cathode of V2 to chassis is about 1.1MOhm.

Rgds

Michael.

[PJL]

https://www.service-data.com/product...48/3615/t13548

V2 cathode resistor (1K) R10 on the Radiomuseum circuit must be faulty.

[PJL]

Lawrence, I see what you mean about VC4 in the Radiomuseum circuit in the regeneration path. I am beginning to think the radiomuseum circuit illustrates a modified version as the connections to VC4 are marked with x's perhaps inferring that the aerial tuning capacitor should be rewired to this position.

[mancunian69]

Sorry, I forgot to mention that VC4 is present but not in the position it is on the schematic.
It is connected directly to the antenna input.

[mancunian69]

Guys, I created a post some weeks ago regarding this radiogram I am restoring for a customer.
The original HMV No.15 headshell was open circuit and could not be repaired.
The Colaro headshell replacement also has issues upon closer inspection.

There are two steel pieces that fit around the coil. One has one of the tiny magnets missing, see attached. There is a larger magnet that sits on top of the steel pieces/coil.

I am getting no audio output from the gramophone. If I gently touch the headshell towards the centre of the platter there is a small amount of sound, but not much.

The original loom had the ground wire connected to one of the coil wires. I have made a new loom and disconnected that.
I can feed a test tone in to the amplifier and can hear it. So I know that the pickup is the issue here.

On a differeent note. I am still getting 6v at the cathode of V2 in gram mode. I have even fitted a replacement MH4 tube and it is still the same. It could be the valve base that's at fault here. I am only familiar with the octal and 9 pin bases in most sets I encounter.
Please advise what type of valve base this set uses and I will look out for a replacement. Having measured the resistance of the cathode pin (with tube fitted) to ground I seem to be getting erroneous readings

I want to know if any member has a HMV No.15 headshell for sale that works. I will place a post in the wanted section for this if need be.

Rgds
Michael

[Gabe001]

Hi Michael, the MH4 valve according to radiomuseum has a B5 base, which I understand is essentially a B4 with a centre pin

I suppose you could ask here to start with, but if you don't find any you can buy valve bases from China. The one in the picture should do, but I've never tried them myself. Hardly a risky purchase at that price though.

Good luck
Gabriel

[PJL]

It seems unlikely to be the valve holder. You need to fix the high cathode voltage before worrying about the cartridge.

Can you give us the MH4 anode, cathode and grid voltages when in gram mode. From Trader 563 have you checked the value of R8 and replaced C10?

[mancunian69]

Ok, I will certainly do some more voltage/resistance checks tomorrow when I've got the chassis out (again)

I now also have a second MH4 tube for side by side comparisons.

I will get back to you in due course.

BTW, all caps and resistors that I can see have been replaced with new components.

The more I study this chassis the more I think that is built to the smaller of the two schematics on the sheets I have taken from the Radiomusem.
The power supply is slightly different on the smaller one, so I may rework it.

Rgds
Michael

[mancunian69]

Hi,
I have taken chassis out and now have the following readings:

V2 in gram mode:

Anode 169v
Cathode 6.2v
Grid 0v

Michael

[PJL]

According to the trader sheet, R8=1K, R9=10k AND R10=50K.
That suggests there is 6.2mA flowing through R8.
V2 has -6.2V between grid and cathode so we would expect it to be cut-off. This is supported by the anode voltage of 169V (trader says 70V) which is higher than the Trader V1 anode voltage. The 6.2mA is therefore not coming from V2 anode.
R4 could be responsible for the current but V1 should also be cut-off.
The intervalve transformer primary is the only other connection to R8 but that is DC isolated by C10.

So...
1. Measure resistance from V2 cathode to chassis (should be 1K)
2. Pull V1 and measure V2 cathode voltage
3. Confirm you have replaced C10
4. Check your wiring and post a picture here

[mancunian69]

Hi,
I have some more readings:

Resistance from V2 cathode to ground, no reading.

V2 anode voltage 166v
V2 cathode voltage 6v with V1 pulled and not pulled.

From the image you can see the two orange caps which are C6 and C11

Rgds
Michael.

[PJL]

The gram input will not work without R8 (1K).

R8 is one of the ones in the cylindrical box. Measure R8 resistance between the pins on top of the box and check continuity to V2 cathode and ground. Having never worked on one of these I am not sure how easy it is to access the resistors in the box.

[ms660]

Seem to have been here before (Post#16):

https://www.vintage-radio.net/forum/...d.php?t=180685

Lawrence.

[Station X]

Threads merged.