New Acquisitions

Hewlett Packard HP8640A


 Due to be delivered in a couple of days is this example of the 8640 signal generator. It looks infinitely better than the very distressed 8640B barn find I worked on a few years back and as you can see above the mains lamp is litand the RF lewvel looks to be nominal. Said to include Option 2 (extended frequency coverage to over 1GHz) it is better in that respect to my refurbished 8640B below.

Read more about this acquisition


 Saba Meersburg Automatic 6-D


  Tim Norman from Ampthill very kindly dropped off this rather fine radio which he'd found in his loft. From the label it's certainly a German import.. maybe brought back to the UK in the late 1950s or early 1960s by a National Service conscript? I hadn't realised it had a motor tuning feature which must have made it an expensive proposition. Our Murphy family radio from the late 1930s had an auto-tune feature but it wasn't fitted in our example.

click the radio above to see its circuit diagram





 Canadian 52 Set ZE12 Power Supply



 Purchased March 2022, this is the matching power supply for my 52 Set


Click to see more

 CJD ELF/VLF Receiver



 I was doubtful when buying this receiver because it didn't look complete. The main clue being a multi-way connector sticking out the back and an apparent absence of valves. There was also its weight. Designed primarily for use in a submarine no expense was spared in exchange for ballast so it tips the scaeles at 97 pounds (44Kgm for our metric friends).

I can see it's going to be a challenge but, having been involved years ago in the design of electronic things supporting the cold war, I feel sort of attached to it. (click and see if this means anything to you)

 To read more about this receiver click its picture.



 I bought this because it looks reasonably complete (except missing the outer case and painted in an odd blue and yellow colours).

When these receivers came onto the government surplus market in the 1950s they were advertised as being admirably suited for modification to serve as IF amplifiers for home brew TV sets. They are rarely seen in an unmodified state. This example has a mains power supply and strangely, a new set of components.

The chassis is fitted with an RF24 marked with numbers 1-5 which could relate to Band I Channels 1 to 5 except the RF unit tuned to lower frequencies as shown below. For TV use an RF25 would be better but I can see through ventilation holes the RF24 has also been fitted with new components.. so has it also been modified for Band I reception?

What confuses me though.. the components are really new.. too new for Band I TV.. so what's its purpose?


Vision MHz

Sound MHz

 RF24 MHz






















Click the picture to read more

 Mystery RAF Radio


  I couldn't resist buying this WW2-vintage receiver as I've never seen one before. It turned out to be quite interesting as it's actually a Bendix MN26-C Radio Compass. From what little information I've found these cover 100KHz to 1500KHz in three wavebands so would make a very good domestic radio, which is how the government surplus market handled them. This example has been modified for use as a domestic radio, rather than the alternative advertised use as a car radio, but still maintaining its remote tuning gearbox but with lots of extra knobs and switches dating from the same era as the set. On the top of the case it carries an RAF crown and what looks like the code 10D/401**.

When I have time, I'll open it up and see why it's so incredibly heavy. Originally it was packed full of IO based valves and a dynamotor for 28 volts DC. That dial carries only 0-100 and could do with a good clean.

Click the radio to see more

**Below, the only external markings, slightly indistict which Alf, G3WSD has decoded as "110D/401".

See three pages of 1949 Government surplus store offerings (but don't forget £10 was a decent weekly wage!).





Teac AG-D200


 Not an ancient collectable radio, but a replacement for my ageing Teac Receiver/Amplifier which has started to give me a headache. Things started to go wrong when electrolytic capacitors in its low voltage power supply circuits began to fail. Then dry joints started to make their presence felt, and then something inside started to get very hot causing it to cut out. Hours with a soldering iron, then the addition of a computer fan running from the amplifier's internal 12 volt supply (via a resistor to limit the voltage and hence fan speed an acoustic noise) fixed the problems, but not long afterwards the thing would fail to deliver any sound unless thumped very hard on its top. Time to replace the whole thing... and I spotted this much newer Teac being sold with a "staticky" fault. Hopefully I can fix this and then perhaps spend time to correct failings on my AG-15D? The new-looking remote control only responded to a few of its buttons so I took it apart and found lots of syrupy deposits on the circuit board. Considering the circuit board is covered by a rubber layer carrying moulded buttons it's puzzling as to how liquid got under the layer of rubber, but careful cleaning restored 100% of its commands.


  The equipment seems to work OK but I looked on the Net for a repair manualand had no luck. I can find an operators' manual but not that for repair. Interestingly, I must have triggered a response because I now get advertising blurb for a new example of the AG-D200... at a whopping £349.99 plus £6.99 postage (opposite). My outlay of £35 for a crackly version seems pretty good! I plugged it in and sure enough I could hear faint crackling on radio reception. The front feet slipped off the front of the bench and the thing bumped down half an inch. I slid it back into place on the bench and the crackles had completely stopped so it looks like an embrionic dry joint or could it just have been poor radio reception?.... I'll lift off its covers and try and spot it. Let's hope it's more repairman friendly than the difficult- to-dismantle AG-10D...

PS. It's just as awkward to take apart as the old model and waggling everything in sight wouldn't make it crackle, although one of the side speaker outputs was quieter than the other and the display is a bit dim.

 Hello Allan Isaacs,

Based on your recent activity, we thought you might be interested in this.

TEAC-AG-D200-7.1-Channel Home Cinema Receiver.PROFESSIONAL.4X HDMI INPUTS
by Teac
Price: £349.99
Dispatched from and sold by D**** (UK).


 Mega328 LCR-T4

A magic meter that can seemingly test anything.

Click it to read more.

 Voxon bass fifty amplifier


This old amplifier was donated by Alan Phillips, a visitor to the Radio Museum carrying duff lift circuit boards needing attention. I'd previously shown Alan my rebuilt Moreton Cheyney amplifier when he said he'd got something similar. It was only later I lifted it onto the workbench when I realised it was indeed similar because of its immense weight and having removed the rear cover and noticed the two hefty transformers.. Those output valves are Pinnacle-branded EL34s, and the name "fifty" maybe implies 50 watts output?



 The valves are a mixed bunch. The EL34s are Pinnacle and a Mullard with the two smaller audio valves both ECC83, again a Pinnacle and a Mullard. The rectifier valve is an EZ80, presumably for the EL34 anodes and on the right, under the chassis, is a selenium rectifier for the ECC83s. There's also a pair of silicon rectifier diodes.. maybe for the EL34 bias supply? Or the other way round as I haven't checked the circuit details.

As you can see below, from the printing on the mains selector panel (missing its shorting plug), the amplifier post dates the Radiospares change to "RS" in 1971 but my Hi-Fi year books are silent on the Voxon name.. at least in 1972/76/ 79. 



 Below a view under the amplifier chassis and then a view from the top. Most of the parts seem to have been sourced from RS. The mains transformer appears to have a date in November 1966 and the output transformer is marked 15 ohms and "785-80" (possibly an RS stock number?).




Audition Instruments Pre-amp/Reverb unit 



 Above...this preamp which came with the Voxon, at first looked like it came from the same manufacturer but when I looked inside it was completely different. It uses a couple of printed circuit boards marked "CDK TP-15A and TP-15B" and Toshiba transistors. From the crude build quality it looks British***. The badge states "Audition Instruments" but I can find no record of this nor the Voxon amplifier, although "Voxson" does appear mis-spelled as "Voxon" in a few places..
 *** You can see the construction in the pictures below. When I attempted to detach the chassis from the case after removing securing screws it wouldn't budge. I used a screwdiver as a lever and forced it out. The self-tapping screws holding the lower circuit board were far too long and prevented the chassis sliding into the case so it had been jammed in place. Wiring conforms to the "scrambled" spec and anyone that's handled Roberts radios from the same era as this pre-amp will recognise the general design and be aware of excellent performance coupled with incredibly poor mechanical design with little thought for a repairman. I'm reminded of a comment by a Plessey mechanical engineer (concerning some satellite ground station equipment) back in the late 60s... "the string is NATO approved string not just any old string".


 Inside the pre-amp case are two early printed circuit boards with the mains transformer on the right.

All the transistors seem to be PNP devices and are germanium rather than silicon based. The pair in the centre, mounted on heatsinks screwed to the lower of the two circuit boards, are Toshiba 2SB462 with the "B" standing for PNP. The case style is TO66 dating back to the 1960s.


Maybe the marking "CDK TP15" means something to somebody? 









 Another item from Dave G3SUL is this BC221 which is a different model to my previous BC-221-AF example seen here. The availability of these equipments back in the 50s, 60s and 70s provided a convenient way of meeting the terms of ones amateur radio license although actually having one to show a GPO inspector didn't always mean it had ever been used.



 Dave also gave me this wooden box. It contained a rather nice 550-0-550V transformer, not the original Type 2 Crystal Monitor, whatever that was?

 HP Spectrum Analyser


 Dave, G3SUL kindly donated this equipment which comprises the HP141T, HP8552B, HP8553B, HP8554B and HP8556B (together with a few very nice 1930s radios which are pictured below, together with a nice clean RA17). As you can see the spectrum analyser is in immaculate condition unlike my usual Hewlett Packard acquisitions. Timing is amazing because I was just about to go searching for a low frequency spectrum analyser with which to investigate my current amplifier rebuild. The 8556 works from 20Hz to 300KHz and includes a tracking generator and I'm hoping this will let me measure the quality of the amplifier in terms of linearity and distortion. Below some radios donated by Dave, G3SUL.




Model 219

Read about the overhaul of a similar example for a customer in 2014




 This generation of radios from 1936 often used a fashionable shiny brass grille over the speaker. I removed the speaker assembly and found the grille was really badly tarnished but turning it over revealed the other side was in fair condition. I glued the cloth in place and fitted the grille which restores the radio's looks.

I use a brushing wax to restore cabinets and once applied looks OK.

Below its unusual audio output valve, an MPT4.



 Ultra Lynx

From 1931




Model 364

from 1936




 A very clean example of the RA17 with S/No. N2866.

 This has a few faults that need clearing up.

See how I'm getting on...


 Skanti TRP8255


 This is the Plessey-badged transceiver fitted in the HDRS, later NCRS, cabins that were supposed to carry army radio traffic to attempt to bring order back to the UK, devastated by nuclear war.

Thankfully the possibility of this ever happening caught MoD off guard leaving the project high and dry.


All advanced projects go wrong because of software problems and HDRS was no different. MoD were more to blame than Plessey because sensible timescales and costs were always secondary to available time and cash.

The more a project is starved of timescale and finance the worse things can get. HDRS wasn't really required but Plessey managed to get the thing delivered under the guise of a sort of plaything for the Army.

Later the whole thing was sold off at bargain basement prices and here's one of the radios I bought from a fellow radio ham...


Read more about the Project.. which for a period I had the dubious pleasure of managing.




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