Record Player Barth Super Schola et Master IV

[Wishiknewmore]

Hello
I am looking for some direction before I power up my latest acquisition
This is a tidy record player with the circuit diagram kindly stuck to the inside of the base, and the main physical damage is the cartridge shell is broken off the arm hopefully a little araldite will fix that.
My immediate questions are about likely need to replace the coupling (that) capacitor (I am assuming that it’s the one marked 22nf from the anode on the ECC83) as well as what, if anything, should I do about the selenium rectifier?
Thanks in advance
Philip

[Nickthedentist]

What a neatly-built machine!

The capacitors look like the Philips "mustard" ones, so will usually be fine.

If the HT seems correct and the rectifier doesn't get hot or smell, I'd leave that too.

Nick.

[ben]

Agree wholeheartedly with Nick. One more thing, check the cartridge has output before gluing the headshell. It might be easier to access/change it in its present loose state!

[Wishiknewmore]

Thank you Gentlemen
I shall give it a whirl sometime this week!
Philip

[Herald1360]

Yes, that's a nice, no nonsense amplifier with the extra triode gain stage allowing "proper" tone controls.

[Synchrodyne]

Yes, I noticed that. With the Voigt-type tone control following the input amplifier, the main amplifier feedback loop is unmolested by the need to include tone controls within it. Another aspect of neatness is the use of a "proper" power supply with a double-wound power transformer.


Cheers,

[Herald1360]

Looked like a passive Baxandall type control to me. The Voigt described in April 1940 WW

https://www.americanradiohistory.com...d_Magazine.htm (page 210 on)

looks similar but not quite the same.

['LIVEWIRE?']

Trevor, I agree with you. My first thoughts were that the control circuit was a Baxandall type.

[Herald1360]

Who's Trevor? Synchrodyne?

[Synchrodyne]

Originally Posted by Herald1360

Looked like a passive Baxandall type control to me. The Voigt described in April 1940 WW

https://www.americanradiohistory.com...d_Magazine.htm (page 210 on)

looks similar but not quite the same.

Good point about the Voigt. I must admit that I am not too sure as to what variations one could make to the original Voigt tone control circuit and still call it a Voigt tone control. In this case I was guided by the precedent provided by Armstrong, who used what it called a Voigt-type tone control on several of its models. The circuit is from the Jubilee Mk II radiogram chassis, but Armstrong appears to have used the same circuit going back to the A10 control unit in 1954.



It could be that even though the circuit was modified as compared with the Voigt original, Armstrong elected to describe it as “Voigt-type” as being consistent with Voigt’s original concept, which was a passive circuit with continuously variable bass and treble controls that moved from lift through cut without any switching. Perhaps “quasi-Voigt” would be a better descriptor for this modified Voigt circuit.

On the other hand, “passive Baxandall tone control” strikes me as being an oxymoron. An intrinsic feature of the Baxandall tone control, stressed in the original article (WW 1952 October, p.402ff), was that it was an active type, built around a virtual earth amplifier, using an RC network that was in both the input and the feedback arms. Baxandall developed it to improve upon the performance that could be obtained from a passive network.

Baxandall himself never published a passive tone control of his own, although he did discuss the Voigt passive type – including the provision of a set of curves - in his later writings, along with his own and others such as the Ambler.

One way of looking at the Baxandall tone control is that it was a frequency-dependent active gain control. Endeavouring to develop a passive version of it would I think be like trying for a “passive active gain control”. Still, we have “passive preamplifiers”, so I guess that anything is possible along the imaginary axis of audio. But “passive” directly contradicts the fundamental feature of the Baxandall control. Possibly whoever coined the name was not aware of the history, and so did not realize that the Baxandall descriptor applied primarily to the active nature of the circuit, and not just to the detail of the RC network.

Incidentally, Armstrong also used the Baxandall tone control, and had done so before its initial use of the modified Voigt-type. Evidently it was not inclined to describe the latter as a “passive Baxandall”.

Originally Posted by Herald1360

Who's Trevor? Synchrodyne?

Pas moi.


Cheers,

['LIVEWIRE?']

Unless I'm mistaken (quite Possibly!) Trevor is Herald 1360. Correct me if I'm wrong

[Heatercathodeshort]

Lovely! I bet it sounds great! John.

[Nickthedentist]

Rather OT, but I found out the other day that Mr Baxandall went to my old school, as did Mr Roberts, the founder of the famous radio manufacturer.

[Herald1360]

Originally Posted by 'LIVEWIRE?'

Unless I'm mistaken (quite Possibly!) Trevor is Herald 1360. Correct me if I'm wrong

Well, yes and no..... I believe I was being referred to as Trevor, but Trevor I'm not.

Look between the wheels on my signature (or carefully at the string of gobbledegook if your browser has stripped out the formatting).

Nick- no idea what your old school was, but I believe Mr Baxandall's son went to the same school as me. At any rate, if Mr. B lived in Malvern in the '60s, he did.

['LIVEWIRE?']

Apologies for calling you Trevor, Chris. I must have had a 'senior moment' when typing that post!!