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-   -   HMV 650 receiver. (https://www.vintage-radio.net/forum/showthread.php?t=194879)

cathoderay57 4th Oct 2022 11:14 am

HMV 650 receiver.
 
4 Attachment(s)
I bought this HMV 650 on eBay. It was complete apart from a missing rectifier valve. It had been partly restored, including fitment of a Gary Tempest replacement dial. I will show pictures including the dial when I have finished the cabinet. I'll say from the outset that my aim was to get this set working properly and to make the cabinet look presentable. It was never planned as a concours restoration, like the fabulous work done by Gary, featured in back-issues of the BVWS Bulletin.

This is a twin-chassis model, with the lower chassis incorporating the power supply and power amplifier. As-found the push-pull power amp had 2 x Tungsram 6V6G beam tetrodes fitted, one of which was virtually zero emission. Out they came and in went 2 x Canadian Mullard 6F6G, NOS and almost direct equivalents of the original pair of KT63. I found a 5Y3GT rectifier and plugged it in. The original electrolytics were long gone, and the chassis had been drilled to accommodate chassis-mounting clips. I have re-used a couple of the replacement electrolytics because they reformed OK, and fitted a new blue LCR reservoir cap. These are a temporary measure to get the set working and I have ordered new screw-fit electrolytics from BVWS Spares, which will look much better. I also noted discrepancies from both the Manufacturer's and Broadcaster data sheets with the addition of an extra preset potentiometer next to the HT fuse. Advice was forthcoming from the Forum (see repair thread) that this was a later modification to introduce silent tuning. The AF driver valve (Z63/KTZ63/6J7G) is muted via a make/break switch while spinning the tuning knob. The switch can be seen in the above-chassis view of the receiver chassis, to the right of the tuning mechanism.

Back on the power amplifier chassis, as a precaution, I replaced the 2 x 500pF feedback capacitors in the output valve anode circuits with new 500V polyester. More on these later.... The rubber sleeving on the HT chokes and output transformer had crumbled so I resleeved them. Then I turned my attention to the receiver chassis. Usefully, the component numbering is the same on the Manufacturer's and Broadcaster sheets, although the Broadcaster has some minor omissions. Some work had been done fairly recently with the fitment of replacement Wima capacitors. Other prior restoration had been done a long time ago including fitment of old-style grey Radiospares capacitors with blue lettering. Some of these tested OK whereas others were leaky and replaced again. I found an initial of a long-lost repairman on the chassis and a date of 24/4/46. The high wattage HT potential divider R8 was already bridged with a 6k 10W ceramic resistor and the other section (R7) was o/c so I bridged it with a porcelain 3.3k. The receiver chassis electrolytic (C18/C24 8+8uF) was completely unmarked and of unknown provenance and so I replaced it with a Plessey NOS 16+16uF because I didn't have any suitable 8+8uF spares. I noticed that the rubber insulated wires from the AF driver transformer were rotten and crumbling, notably the red and yellow ones. I pulled them out and then discovered that the terminations at the transformer end were sealed in tar (should have read Gary's article first :dunce:). By then, the sin was already committed but I manged to reseal the ends of the 7 wires where they entered the cable duct into the base of the transformer using silicone sealant, then cut the wires one by one and soldered on replacement neoprene insulated wires using heatshrink to cover the joins.

cathoderay57 4th Oct 2022 11:36 am

Re: Hmv 650
 
2 Attachment(s)
Time came to power up. It worked, just. I could hear strong stations such as R5 Live only if I turned the volume up full. Finger prod test on the gram input produced a very loud hum, and so the fault lay further back. I measured the anode and screen voltages of the receiver chassis valves and all read a bit high. Was the AGC biassing them hard off? The bias voltage at pin 12 of the power unit plug measured -4.8v (spec -4.5v) so it didn't appear to be that. To cut a long story short, it was an own goal. In pulling out the wires to the AF driver transformer I had accidentally broken the connection between the final IF transformer (L30) and the anode of the detector diode. Resoldering it brought back loud reception on LW and MW and a couple of stations on SW. There was a low crackling noise from the speaker as soon as I switched on, and before the output valves had warmed up. I feared the worst - internal shorts inside the output transformer windings? Fortunately not. One of the new replacement 500pF 500v poly filter caps in the anode circuit of one of the output valves was leaking causing conduction via R41/R43. Disconnecting both resulted in no crackling but a high-pitched whistle. Refitting one restored silence. Refitting the other restored crackling. Replacing it restored silence once more. Phew, a bit of a relief. The magic eye is deflecting only about 50% on strong stations. As-found, the second half of the Y63 grid potential divider, R14 (2.3M) was missing so I had replaced it. I doubt if the omission was intentional. Next I'll do an RF alignment (the IFs seem pretty much OK so I'll leave them alone). Hopefully that will restore the deflection. If not I'll have to play around abit more with the biassing. Then if all goes well I'll tackle the cabinet. Cheers for now, Jerry

cathoderay57 4th Oct 2022 9:25 pm

Re: Hmv 650
 
The radio responded well to RF alignment, albeit only slight tweaks were needed. The magic eye deflection increased a little bit but not enough to make me happy. I could have messed around with the biasing or altered the ratio of the two 2.3M potential dividers R13 and R14 that determine the Y63 grid voltage. Instead I swapped the Y63 for a NOS CV51 (Y65) that only requires half the grid voltage for FSD. It still won't deflect fully but is good enough. I will probably disable the silent tuning feature because it is irritating when tuning around on SW. Other than that, it's a fantastic set and I am delighted with it. It's going to take a while to sort out the cabinet but I'll post some pics when it's done. P.S. in Post #1 I said the PSU/PA chassis was the lower chassis; In fact it's the top one. Cheers, Jerry

turretslug 4th Oct 2022 9:28 pm

Re: Hmv 650
 
Great work Jerry, and what a magnificent radio- not a project to undertake lightly! It always brings a little smile to find evidence of previous competent repair to vintage kit that was obviously done long after its original purchase- it suggests to me that something was sufficiently valued and appreciated that the owner was prepared to invest in keeping it going.

Bit of a pain to find that a new component was faulty though- I try to avoid the paranoia of testing every new component before use, but I sometimes do when a job is too inaccessible, awkward and painstaking to have to repeat. Just occasionally, something has been duff from new, and a certain law tends to apply regarding its difficulty of replacement....,

Colin

slidertogrid 4th Oct 2022 11:30 pm

Re: Hmv 650
 
Nice Job! :clap:
Rich

cathoderay57 11th Oct 2022 12:33 pm

Re: Hmv 650
 
Thanks for the praise. I have stripped the cabinet and I am currently respraying it. Meantime I looked at the cabinet label and it is a P/1 variant. According to Gary Tempest's article in the BVWS Bulletin Autumn 2010, that dates it to 1936, but I'd have thought that was a bit early for international octal valves. I'm not saying Gary is wrong, and as far as I know IO bases were first introduced by the Americans in 1935 but I would have thought only a limited range of valves would have been produced in the early years. Thoughts? Jerry

stevehertz 11th Oct 2022 12:44 pm

Re: Hmv 650
 
Well, I can't answer your (valve) query in a factual manner, but HMV were always at the cutting edge of technology, so given that the radio was made in 1936, ie a year or even up to say 18 months after the valve range was released, then it's quite feasible and of course you have the proof before you. Otherwise it's most unlikely that someone has changed the valves and bases. To my knowledge the 650 used the same valves throughout production, that is to say, international octal.

Paul_RK 11th Oct 2022 1:52 pm

Re: Hmv 650
 
My copy of Receiver Specifications and Prices 1935-40 has gone to ground again - I'm nearly sure I was looking at it just a month or two ago - but my dodgy memory assures me that this range of sets (I just have a Marconi 563 radiogram) was only released in or around August 1937.

Paul

cathoderay57 11th Oct 2022 4:49 pm

Re: Hmv 650
 
Just found these pages at the Valve Museum, which I didn't know existed. It turns out that American equivalent valves including 6F6G (=KT63), 6J7G (=Z63/KTZ63), 6L7G (=X64) were around in 1936 http://www.r-type.org/inx/inx1936.htm but the Marconi numbers used in this set do not seem to have appeared until 1937 http://www.r-type.org/inx/inx1937.htm and so Paul is probably right :thumbsup: Cheers, Jerry

cathoderay57 13th Oct 2022 9:17 pm

Re: Hmv 650
 
3 Attachment(s)
Just about done refinishing the cabinet. Waiting for some white waterslide paper to do the Nipper transfer. Also ordered some replacement 3/8" No.3 woodscrews for the Bakelite frame around the tuning window. Couldn't find japanned screws so using bright brass but can always paint the screws with black enamel. Pics attached. Jerry

stevehertz 14th Oct 2022 7:35 am

Re: Hmv 650
 
Jerry, congratulations on a truly excellent refinish job there. Sets like that with nooks and crannies and grooves are very difficult to prep, but it looks like you did a good job there.

What was your stripping/prepping procedure out of interest? and what have you used for the lacquer?

That set will occupy pride of place when it's done I'm sure!

cathoderay57 14th Oct 2022 9:02 am

Re: Hmv 650
 
Hi Steve, thanks! I used Nitromors varnish stripper wearing a mask and with good ventilation in the garage, also using wire wool. Cleaned off the resulting sludge with white spirit. Followed with a very light sanding using fine grade paper. I used Mohawk Van Dyke brown toner applied with a brush to the crossbar below the speaker grille, which didn't appear to be veneered. Then sprayed the whole cabinet with RustOleum clear semi-gloss spray lacquer. When hardened I finished off any areas that were dulled owing to mottled overspray using T-Cut. I hand painted the feet and top panel edging using black enamel. Cheers, Jerry

stevehertz 14th Oct 2022 9:19 am

Re: Hmv 650
 
I'll take note of that. :)

Gabe001 15th Oct 2022 7:11 pm

Re: HMV 650 receiver.
 
It's looking great Jerry. Nice job on the cabinet too.

cathoderay57 24th Oct 2022 8:52 pm

Re: HMV 650 receiver.
 
3 Attachment(s)
Had a bit of a hiccup. I fitted a good U50 rectifier in lieu of the low-emission 5Y3GT that I had been using up to now. It pushed up the HT a bit but brought the unwelcome side effect of causing SW1 band (34m-107m) to go into spurious oscillation - magic eye FSD, audio silent and Vbias (measured at R39) up (down?) from -3.6v on MW to -8.5v on SW1. It became obvious that it was V2, the mixer, X64, that was taking off, but only on SW1. Having sought advice from Gary Tempest, who has restored a number of these sets and written the excellent BVWS Bulletin articles, in the end, having checked the obvious biasing components, it boiled down to a choice between full realignment (no, thanks), adding a 100k grid stopper at the top cap of the X64, or trying a replacement X64. Well, I opted for the easy option of trying a replacement X64, which worked perfectly, maybe because the replacement valve had a little less gain at the SW1 frequencies? I had tested the original valve on my VCM163 and it measured 100%. I also tried the troublesome valve in my Marconiphone 538 and it worked perfectly on the same band and in a similar circuit. ??? Many thanks to Gary for his advice and for sending me some japanned screws for the tuning dial window frame, plus jpgs for the Nipper transfer. The transfer worked out OK using white waterslide paper and an inkjet printer, sealed once dry with 3 coats of lacquer per instructions, which stops the ink from bleeding, and also reduces the propensity of the transfer to curl up when wet. I've attached some final pics. I think that's all, folks. Cheers, Jerry

stevehertz 25th Oct 2022 8:04 am

Re: HMV 650 receiver.
 
Excellent job Jerry - from one 650 owner to another!

Gabe001 25th Oct 2022 7:25 pm

Re: HMV 650 receiver.
 
Wow Jerry that's stunning. Glad the waterslide transfer worked out.

The dial lights up beautifully.

turretslug 25th Oct 2022 8:24 pm

Re: HMV 650 receiver.
 
Ooh, that's sumptuous Jerry, surely a "pride of place" job. Well done, Colin.

cathoderay57 25th Oct 2022 9:13 pm

Re: HMV 650 receiver.
 
Thank you!

Hybrid tellies 26th Oct 2022 9:53 am

Re: HMV 650 receiver.
 
That looks really good and with the faults you have cleared most certainly sounds as good.


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