Hmv 1115

[Beardyman]

The next victim has surrendered to the multitudinous tools of the examination table.........
That was a bit OTT but you get the general idea!
Well, what a difference from the Bush DAC90A.
The HMV (February 1946) gives very much the feel of a kit?
Findings so far are that both the scale lamps (5V 0.15A?!?) are blown.
The dropper (although good) seems to have seen a hard life, maybe a "wattless dropper" for the main resistance would be in order......we shall see, it's early days.
There is a LOT of waxies in there, how they crammed 6 valves in there AND thought it was a good design is a bit beyond me.
All the rubber covered wiring is shot, it'll be replaced with PTFE or TEFLON, for the very hot parts it's silicone all the way, luckily there's no shortage of either in the scrap bins at work!
Why oh why did they notate every capacitor value in uF?
And why do the Trader Sheets never give the working voltages?
There's a waxy in the chassis rated at 750VDC?!?!?
Then again there's an 8uF capacitor rated at 175VDC, go figure.
I'm guessing it's more a question of what they could get hold of at the time as it was just after WW2 ended. The 32uF capacitors have both leaked electrolyte quite badly.
More exploration on the morrow.............

[ms660]

Originally Posted by Beardyman

And why do the Trader Sheets never give the working voltages?

There was no need, because any service engineer worth his salt would know the maximum voltage that the capacitor would be subjected to in the receiver.

Lawrence.

[Herald1360]

The 750V waxy could be either across the output transformer primary or a mains filter of some sort. If the latter, replace with X or Y type depending on what it's doing.

HT on these will be fairly low thanks to the half wave straight off the mains PSU so an 8uF 175V decoupling capacitor for V3 anode supply sounds reasonable.

[Herald1360]

Originally Posted by ms660

There was no need, because any service engineer worth his salt would know the maximum voltage that the capacitor would be subjected to in the receiver.

Lawrence.

And in any case, it would be marked on the component in question!

[ms660]

Originally Posted by Herald1360

And in any case, it would be marked on the component in question!

But in some cases some of the markings might not have survived as readable!

Lawrence.

[ukcol]

Originally Posted by ms660

But in some cases some of the markings might not have survived as readable!

I have come across "waxies" that don't have any voltage markings on them at all. I remember in particular changing some in a Murphy radio, they were marked only with their capacitance value and "type 1049" or "type 1618".

The required working voltage will be determined by the maximum voltage that is likely to appear across the component in a given circuit, plus a sensible safety margin. You would then pick the next "preferred" working voltage up, in the range available.

If you have determined that you need a (say 400v DC) working capacitor there is no problem with fitting a higher voltage one (say 600v DC) providing physical size is not a problem.

If in doubt ask here.

[Beardyman]

Oddly enough I've found a couple of the type 1049's that UKCOL mentioned!
As the smoothing caps are rated at 175VDC anything over 250VDC will be able to cope. And there are several others that the markings are just about legible, with the careful application of a heat gun, voila! all becomes plain again as the dust is soaked into the wax! However, the markings can also slide off!
Right now I'm compiling a spreadsheet to keep track of things & the rain is pouring down........again!
Thanks for all your input as always, much appreciated.

[Boater Sam]

Please. Please, don't just do a blanket change of waxies, get it working first, then one at a time is the way. Please!

Change no silver mica wax caps unless they are definitely duff, you'll loose the alignment.

[Boater Sam]

A good solidly built set, push pull output will rattle a few windows. Post war, 1946, austerity period but HMV still did a good job.

Details here if you have not found them yet,https://www.radiomuseum.org/r/hismasters_1115.html

Service sheet should be up top of page in the data library.

Old type valve line up should cause you no problems, don't pull them out by the glass, that may need re-gluing to their bases.

[Beardyman]

Many thanks Boater Sam, I'll be sure to check each one although most of the resistors are at the far end or over their tolerance. The electrolytics are all leaking. I've got a MEGGER which goes from 50V up to 1KV & a FLUKE LCR meter so I should be able to weedle out the iffy waxies. I've already got the trader sheet so will spend this afternoon collating information & reading through various threads. Have a good afternoon one & all.

[Beardyman]

Well the HMV1115 is finished & it does sound GOOD with plenty of volume!
The volume control (with switch) had gone open at the very beginning of its travel, just a tiny bit further & it was blowing the windows out!
Found a replacement without too much trouble then the wave change switch decided to act up, I was thinking I would have had to replace it with a modern one but decided to have a thorough look at the thing under the magnifier. Would you believe it? It was caused by a dry joint that had been there since the set was built!?!
Overall I'm very pleased with the way it turned out, its probably not for the purists out there but the other half loves it.

[PaulR]

Congratulations. It is a good looking set. I once had the radiogram version but gave it away.

What is next??

[Sideband]

You're getting good at this!! Well done and a good looking set as well (with the power to back it up)!

[Beardyman]

The next set is an Etronics RA640.
I got the trader sheets from this forum but even those are a little scant on detail, apparently the chassis was also used for a radiogram known as the QGA532 which adds a little more information. It was in a bit of a sorry state when I got it, rusty chassis, case thoroughly beaten up, tuning scale cracked & tuning cord broken! I like a challenge! Oh, and both the smoothing caps are leaking like sieves despite a lengthy effort to reform them. Luckily I have access at work to some very fancy power supplies (TDK-Lambda GEN600-2.6). Still waiting for one to be scrapped off!............
Thanks for your comments, they are most welcome.

[crackle]

That's an interesting schematic you have on your PC screen, do you turn them negative.

Mike

[raditechman]

Nice to see the restored HMV 1115. I have one in my collection. Like yours it needed a complete rewire.

John

[Beardyman]

Hi Crackle,
Yes, I usually scan the trader sheet or snip the schematic in the PDF then, if there are two sections, join them together then edit the schematic to make it more readable. I suppose I've been spoilt with industry standard diagrams! I'll often add the component values & any mod's the manufacturers sometimes include. Its more for information & preserving the readability than anything else. I also compile spreadsheets for the components & where they can be sourced as well as a "restoration manual" or what was done, why & of course pictures! Its a habit I've got into, I document everything I do. It may benefit the next owner (if there is one) but it's more likely going to nudge my awful memory!