Rectifier used in HMV 2022 Record Player.

[Murphyv310]

Hi.
I've looked at the circuit. From the cartridge to the grid of the triode section of the ECL86 it looks to me like a very lossy circuit. The Volume control is only 250K which is crazy and the Bass and treble controls will add losses, R1 330k will need to be kept in circuit or bass will drop, same with R5.
R2 (bass) & R3 loads the cartridge (at all frequencies but more so the bass) and the lower the overall resistance when adjusting the bass control the bass tails off as it should, R5 then passes the signal to R6 the volume control and C2/R4 the treble control.
The cartridge HAS to be a high output type and if down at all volume will be poor.
The input impedance is very high on the triode grid. Check R7 (10Megs) and make sure it's not gone high, check C4 & R11.
Go round all the earths again and make sure the screened leads are up to the job. Substitute the ECL86 to confirm it isn't the culprit of the hum, if the rectifier was duff HT would drop to around 170v or below, don't forget a duff valve or leaky C5 will make the pentode section pull more current and cause the HT to sag.
As a last resort a small reduction in negative feedback will give you a bit more gain, try increasing R12 to 680 ohms.

Oh and what is the HT on C4? A DMM will be fine checking this voltage as will it be on C8.

[Mark Hennessy]

Although it's easy to criticise from afar, I think it's fair to assume the designers knew what they were doing. Obviously the unit worked well enough originally.

The various vintage forums are full of threads about these old cartridges degrading and post #29 suggests that the amplifier is working well, so a replacement cartridge is surely the next course of action?

When the output from the cartridge is at the correct level, there's every chance the hum will be much less objectionable because the volume control will be at a lower setting for the same audio output. Some hum was usual with these sorts of machines anyway.

Regarding earlier comments about rectifier reliability, I nearly always have to change them in Hacker Mayflowers, for what that's worth.

[Murphyv310]

Hi.
I certainly agree Mark. The unit would have worked well when new and these old Crystal cartridges do "go off" overtime.
What though is available now? I recently bought a Ronette copy cartridge and although the output and quality were reasonably good it didn't track well at all, it was a mono, stereo compatible cartridge, it did seem high compliance though which I believe it doesn't match with high mass arms., or have I got it the wrong way round? Anyway it did seem extremely stiff if you know what I mean.

[Terry]

A high compliance cartridge has less stiffness than a low compliance one. If you fit one in an arm which doesn't have very low bearing friction, as the record plays the arm stays still and the stylus is pulled sideways as the record rotates until push comes to shove and the stylus jumps out of the groove. I suppose it could just as easily 'twang' the arm sideways in a series of jumps if the tracking weight is too high!

I don't know how much the arm mass matters but it seams reasonable to assume that the higher the mass, the more bearing friction there will be.

Certainly, I've never seen an HC cartridge in anything other than a very low mass arm.

I suppose that, if you fit a low compliance cartridge in a lightweight arm that there might be a tendency for the groove to vibrate the entire arm rather than just the stylus.

I don't think I've ever seen a stipulation that an HC cartridge must be fitted in a low mass arm, though.

[Murphyv310]

Thanks Terry.
Snag is what's decent out there now. Prices are high too.

[Terry]

I did have a box full of NOS cartridges, including several Sonotone 9TAHC with the modified one hole fixing for Garrard arms but I can't find it any more!

I took it to a couple of VRAT meet-ups together with a box of NOS styli which I can't find either!

I can only assume that I either forgot to bring them home or left them in someone's car - probably Mike's (Crackle).

[Murphyv310]

The Sonotone 9TA series are brilliant cartridges. I have one in my Pye black box. It does need a preamp to drive the amp properly. If you look at the input circuitry Terry of Old Sparkys HMV the bass control uses the operating conditions of the Crystal cartridge for it to work. Using a ceramic cartridge would then alter this circuit. Let's hope he can find a good replacement.
Snag is the repair will be getting expensive now with parts and labour.

[Old Sparky]

Before even thinking about a replacement cartridge, I'll try a known good ECL86 in the player. If it continues to work for maybe an hour or two without the hum & noise, then a replacement valve will suffice. I haven't logged in detail how much time I've spent on this, mainly due to having to replace the valveholder, but it must be several hours over three or four weeks! (Don't like to be beaten by such a simple circuit!!!)

[Mark Hennessy]

Why don't you measure the output level of the existing cartridge? You have a 'scope, I seem to recall

[Terry]

In my last PM I said: "The process for inserting pictures into your post is very similar, so you might use that."

Sorry, that is wrong.

Like inserting a link it will ask you for the url which is why you need to add the picture as an attachment!

Sorry for the confusion.