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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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21st Feb 2021, 9:09 pm | #1 |
Triode
Join Date: Feb 2021
Location: London, UK.
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Sugden preamp WAL AC Farnell.
Are there any Sugden fans who might be able to shed some light on this unit?
Neat wiring, soldering and the feeling throughout of a hand assembled unit but would appreciate some more insight and background. I think WAL stands for Wellington Acoustic Laboratories, more than that I don’t know. Would be grateful if anyone can comment on its likely sound quality. To work as a phono preamp would it require an outboard RIAA? What would be its best role in a system? Could it work as just a sitting box? I haven’t yet fired connected it up, are there any readings I could check with a DMM? |
22nd Feb 2021, 1:11 am | #2 |
Octode
Join Date: Mar 2016
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Re: Sugden preamp wal ac farnell
First thing: check earth continuity. If you have a PAT tester, that's a good idea.
Do you have a variac? I would strongly recommend switching it on by gently ramping up the voltage on one. 'Disc' input suggests that it has some kind of replay EQ in it. As to whether it's the conventional type of RIAA, you will only be able to find out either using a reverse-RIAA filter (easy to make, and probably cheap on evilbay); or using a test record (the latter won't be accurate, as you'll be measuring anomalies / resonances in the cart / stylus / preamp combination ). If it's easy to do, you could detach the PSU from the rest of the circuitry and power the PSU on its own. You could measure its output, and you could also try powering the PCBs from a current-limiting lab PSU (while watching its output on a scope) on their own. As an early solid-state preamp, I would very much doubt if it takes more than 50mA per PCB. Be cautious with I-limiting to begin with. Some of those yellow axial caps will need checking out. They can start to pass DC at this age. If it's easy to do without hurting the PCB, you can lift a leg and measure their R. It ought to be high: preferably in the Meg Ohm range. It is designed to connect to some kind of control amp or level control, so you'll need to make something up to go between it and a power amp. Try it on a line input on an integrated amp first. Before you connect it to anything, check all the inputs and outputs for DC offset. Look at them on a scope as well. edit: This is quite likely designed for a ceramic cartridge, in which case a typical reverse RIAA won't work with it, nor will a modern cartridge. My expertise doesn't extend to ceramic carts, but there are many members here who will know how to handle it. NB - I think it's quite elegant. I look forward to finding how it works out. And another edit: Sugden is still going. Why not shoot them an email? I'm a fan of their work. They seem like a good company to me. Last edited by knobtwiddler; 22nd Feb 2021 at 1:24 am. |
22nd Feb 2021, 2:39 am | #3 |
Dekatron
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Re: Sugden preamp wal ac farnell
The yellow axial caps look like Mullard Mustards to me. I'd be surprised if they were leaky and even more surprised if they were leaky enough to matter in a relatively low impedance solid state circuit.
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22nd Feb 2021, 7:56 am | #4 |
Hexode
Join Date: Nov 2010
Location: Sheffield, South Yorkshire, UK.
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Re: Sugden preamp wal ac farnell
Unusual unit with it having a microphone input as well as disc and tape, the microphone has left and right too, the case with the outward facing wings for screwing down to hold it in situ, maybe used in an educational, theatrical or something similar setting.
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22nd Feb 2021, 10:05 am | #5 |
Rest in Peace
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Re: Sugden preamp wal ac farnell
Anyone got a Farnell catalogue of that era? I don't know when the company changed from A.C. Farnell to Farnell Electronic Components or whatever it became next. Might it have been a special commission for Alan Farnell?
The Erie / Hunts electrolytic cap is interesting in having a date code of YYA = 009. It must be a YMM code rather than WWY as there is no week 00, and if it has Erie branding it's late enough to be YMM anyway. That puts it at September 1970, which tallies with the only Philips / Mullard code I can see in the pics B0S which is April-June 1970. Perhaps you can read others. As per Herald1960 it is most unlikely there is anything wrong with mustards. |
22nd Feb 2021, 10:44 am | #6 |
Dekatron
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Re: Sugden preamp wal ac farnell
The mullard mustards are polyester dielectric and very unlikely to be a problem. The axial electrolytic caps could do with checking, particularly since the superb construction unit is over half a century old (eek!)
Craig |
22nd Feb 2021, 12:30 pm | #7 |
Octode
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Location: Owston Ferry, North Lincolnshire, UK.
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Re: Sugden preamp WAL AC Farnell.
A.C. Farnell were based in Sheffield, where as Farnell Electronic Components were based in Leeds and were totally seperate companies, although they were set up by members of the same Farnell family. A.C. Farnell were more into brown goods and service spares, I used to buy PL519 and PY500A from them, as their valves were g'teed and seemed to be of a higher quality than a lot of others at the time. I think that A.C. Farnell ceased trading a lot of years back. Farnell Electronic Components did and still do mainly electronic components.
The preamp of the OP was probably built for factory usuage to supply music and announcements over the 'in house' entertainment system for the factory workers. It may also have been used in warehouses, larger offices and shops for similar purposes. Dave |
22nd Feb 2021, 12:40 pm | #8 | |
Octode
Join Date: Mar 2016
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Re: Sugden preamp wal ac farnell
Quote:
Craig makes a good point re: electrolytics. More reason to use a variac when turning it on, unless you plan to shotgun re-cap them (which could irk some around here!). I haven't encountered a ceramic cart since my age was in single figures. Am I right in thinking it most likely is for ceramic? |
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22nd Feb 2021, 12:49 pm | #9 |
Dekatron
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Re: Sugden preamp WAL AC Farnell.
Well there are two polystyrene capacitors in there of clearly different value. So I suspect that it *might* have RIAA correction - implying it equally *might* be moving magnet and not ceramic.
Without tracing the circuit, or measuring its frequency response it is difficult to be certain Craig |
22nd Feb 2021, 12:51 pm | #10 |
Octode
Join Date: Mar 2016
Location: London, UK.
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Re: Sugden preamp WAL AC Farnell.
The gain will be different for ceramic, right? They are a lot louder than the typical 4mV from a MM. I think you are probably right, though. You can make a fairly effective RIAA with 2 caps.
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22nd Feb 2021, 12:59 pm | #11 | |
Octode
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Re: Sugden preamp WAL AC Farnell.
Quote:
I think that is quite probable. No tone controls, Jack sockets on the front, no Tuner input wouldn`t be a great spec for a domestic Hi Fi pre amp, even in the sixties. |
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22nd Feb 2021, 1:40 pm | #12 |
Hexode
Join Date: Nov 2010
Location: Sheffield, South Yorkshire, UK.
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Re: Sugden preamp WAL AC Farnell.
I thought they were jack sockets, but looking closely, they look more like phono type, top row of sockets, the far right one, you can see a gap around the edge through fascia, and the shadowing of said socket.
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22nd Feb 2021, 1:54 pm | #13 |
Nonode
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Location: Stafford, Staffs. UK.
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Re: Sugden preamp WAL AC Farnell.
It seems WAL is Wellington Acoustic Laboratories. Seems to be for music / PA rather than home as others have suggested.
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22nd Feb 2021, 2:37 pm | #14 |
Triode
Join Date: Feb 2021
Location: London, UK.
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Re: Sugden preamp WAL AC Farnell.
What a superb forum! Just excellent.
Thanks to everyone who's contributed so far. I now know a great deal more than I did yesterday.. Further contributions of course welcome. |
22nd Feb 2021, 3:17 pm | #15 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
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Re: Sugden preamp WAL AC Farnell.
Looking at what I can see of the board, it looks like this could be based on the Bailey three transistor design, which appeared in December 1966 WW. This had the innovation of feeding the frequency selective feedback from an emitter follower rather than the two transistor gain cell. (In addition, one of those transistors looks like a Ferranti E-line, now made by Diodes Inc. One of the secrets of low voltage noise designs are the E-line devices)
https://worldradiohistory.com/UK/Wir...ld-1966-12.pdf It was further improved byWalker WW May 1972 https://worldradiohistory.com/UK/Wir...ld-1972-05.pdf But that post-dates the OP's unit. Craig |
22nd Feb 2021, 3:28 pm | #16 | ||
Rest in Peace
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Re: Sugden preamp WAL AC Farnell.
Quote:
Quote:
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22nd Feb 2021, 3:51 pm | #17 | |
Moderator
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Re: Sugden preamp WAL AC Farnell.
Quote:
This was done by designing in excellent current sharing mechanisms and low base-spreading resistance. Coincidentally, this also made them rather good for low noise capabilities in low impedance environments. It took a while for this to be recognised, but it's real. Low noise people designing dynamic microphone inputs eventually found that Rohm made a range of low spreading resistance transistors for the motor drive market, and that these parts were about the best for their work. Of course, Rohm obsoleted them when they saw the motor market drop off as it changed to MOSFETs and IGBTs. Who'd have thought that tough motor drive transistors would have a sideline in the most delicate applications? David
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22nd Feb 2021, 4:06 pm | #18 |
Dekatron
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Re: Sugden preamp WAL AC Farnell.
The other characteristic is low Vce(sat). I have measured 6mV on some of the current E-line devices even at a few mA Ic. Of course this is a needed characteristic for applications like stepper-motor drive. There is a definite correlation between Vce(sat) and en.
The rbb' of some of the E-line devices has been measured (HH Ed 3) at sub 2-ohms with very low 1/f noise corner, better even than the legendary and long obsolete Rohm parts. Diodes Inc have now recognised the low noise performance of their E-line devices, and list as one of the applications low noise audio. The disadvantage is of course high capacitance, because of the extended (interdigitaged) junction area. Craig Last edited by Craig Sawyers; 22nd Feb 2021 at 4:14 pm. |
22nd Feb 2021, 4:18 pm | #19 |
Dekatron
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Re: Sugden preamp WAL AC Farnell.
Just found my measurements. Cobo is in the range 60-100pF at 10V Vce, which means that they really need to be cascoded, or used common base.
Craig |
22nd Feb 2021, 4:22 pm | #20 | ||
Nonode
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Re: Sugden preamp WAL AC Farnell.
Quote:
https://advanceproductservices.co.uk...s/our-history/ Not hard to imagine that there could have been a business relationship between Sugden and Farnell in view of their close geographic proximity. Worth noting too that R E Sugden was very much focused on good quality audio equpment. Alan |
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