2 valve amp in record player, humming since moving home

[gazz]

My GF has a BSR UA-25 record deck, built into a suitcase record player with a little 2 valve and one condenser amp,

she says it worked fine except the auto play/change mechanism wasnt quite right (dried up grease and some adjustments needed) but since she moved house, it developed a bad hum, 

The hum starts about 3 seconds after turning it on, and get louder... as the valves warm up, 

it's a very simple circuit... BUT i have never played with a valve amp before, 

it takes 230 volts with no earth from the mains plus down some old figure 8 cable (looks like white speaker wire) straight to the main switch, which is part of the volume knob, 

Then it goes to the motor, which has a 100Ma winding to output 90 volts (i know this as a label on the wire says so :) 

the 90 volts goes to the valves, a few resistors and the big metal condenser, there is a tone pot in the circuit, then a speaker matching transformer and a 3 ohm speaker, and that's it apart from the stylus and what ever kind of pickup is used (peizo i believe) 

i presume it never had an earth connection, no obvious earth tag inside the unit, the case is wooden so no chance of touching live parts... except of course the deck is metal, but hey, it was built in the 60's i guess, electricity wasnt that dangerous back then :D

I'm not sure which bits i should wiggle, prod or probe to see if the hum gets louder or quieter, 

could it be a valve dying? or the condenser/capacitor showing it's age (metal can 3 solder tag jobbie) or something happened in the motor as that's where the 90 volts for the valves comes from, 

something has happened in it's transit to cause this hum.... but it's a portable record player designed to be lugged about like a suitcase, so why had it done it now.... no obvious wires off their solder tags, or anything shroting out, and as no earth to the unit, no earth wire off as i suspected at first, 

[Pat McDonald]

Probably not the valves themselves. If they were dead or dying then they would not amplify at all.

If it's a mains electricity style 50hz hum I would expect reasonance from a lead. I would try the leads connecting the condensor or coils might have loosened a bit. Actual fix not so hard, blob of hot glue in the right place.

Finding the lead or wire (maybe component body) that is rrasonating is the hard part. Rubber gloves recommended as you try wiggling each lead and wire to shut off the hum.

It could also be caused with cross talk from neon lighting tubes, fridge or similar at the new location, in which case fitting a shield inside the unit and connecting an earth would help sort it. If the cross talk is coming through the mains wires though, that could be a sympton of a fault elsewhere. Fitting a choke to the mains input would again reduce or remove the problem.

Ask them if they have any neon tube lighting, if yes then a choke should be your first fix. Won't hurt, might cure it totally.

[Vicki W]

My Dad builds and repairs valve amps. He's coming in with me sometime next week so can have a look/chat with you then if you're struggling.

Until then here's what he's got to say.

--
Could be any number of things TBH. But seems odd that it's started up after it's been in transit. chances are it's something worked loose but could be a dud PS cap or rectifier.
Check the input lead (if there is one) between the arm and the actual amp, especially any connections. If there's a phono plug/socket anywhere in the line make sure the outer edge of the plug makes contact with the outer of the socket, squeeze it slightly oval if you have to.
You can give the valves a wiggle in their sockets in case it's a bad connection, be careful not to smudge/remove the chalky white lettering when you're touching them as you'll probably need to identify them at a later date.

Does the hum level increase/decrease with the volume control?

[Gazz]

Awesome, thanks for the advise guys,

I've been messing about freeing off the auto play mechanism first, as
mechanical stuff is what i do best,

So i havent really played much with the actual record player running,
It's never had an earth connected to it, and i've read that sometimes it's
not wise to retro fit an earth if it's a live chassis amp, the flat has RCD
protection, something they didnt have in the 60's when they made this thing.

I've found out the amp is really a 1 valve amp, the other valve is a
rectifier valve, so it's a rectifier, and amplifier valve, and a condenser,
A 'UY85' a 'UL84' valves, and a 'HUNTS capacitors' metal can condensor
jobbie, 32uf @ 275 volts, 16uf @ 275 volts, and a 25uf @ 25 volts, 'can
negative'

The hum sounds like a mains hum, and it gets louder/stronger during the 5 or
so seconds i have had the unit powered up, so i havent touched the volume of
tone pots to see if it changes with their position, but it's is a really
strong offensive 'hum' if tht makes sense, not a gentle transformer type
hum, a relly clicky noise i really dont like at all.... worried it'll get
louder and louder then go bang, but my partner says she has played records
whilst it's humming... but i can't do that as i think too much about what
could happen :)


--------------------------------------------------
From: "Vicki W" <vicert...@gmail.com>
Sent: Friday, May 15, 2015 5:28 PM
To: <notti...@googlegroups.com>
Subject: [Nottinghack] Re: 2 valve amp in record player, humming since
moving home

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[Vicki W]

I'm almost certain these were indeed a 'live chassis' design, ie no mains transformer and hence everything powered directly from the live and the chassis is connected to neutral. You should at least check the wiring at the plug and input to the set because if the L+N are transposed you will indeed have a LIVE CHASSIS! Unplug it when working on it if possible and preferably connect via a 240V isolation transformer if you have to work on it while plugged in.
My first area for investigation for faulty components would be the capacitors, they usually fail first due to age and would really need replacing by now anyway. use modern smaller ones of the same or higher rating, if there's not enough room inside the chassis you can open up the old cap can and fit them in there to keep an authentic look.

[Gazz]

Thanks for the advise,
i've been treating the chassis as live even if it isnt, not quite got my
rubber gloves, rubber soled boots and 3 foot long insulated screwdriver in
use, but i'm unplugging it each time i play with anything on it.

Think i have deduced the condensor/capacitor thingy is gone, some bulging of
the rubber bung and i am getting weird readings on my meter, there is only a
rectiier valve, amp valve and a few resistors left in the whole circuit...
well, a capacitor on the tone control too,

the buzz / hum doesn't change with volume,

Now the condensor is one of those old 3 capacitors in one can jobbies, as
this amp is hidden inside the case, i guess i can just replace it with 3
modern caps, but believe the ripple rating is important,

But if i could get a new can capacitor unit i'd be happier as it'd be
keeping the record player more origional,

Dont suppose anyone knows if there are likely to be any 3 in 1
capacitor/condensor cans in the hackspace? or where i can get one from?

It has the following markings on it:

Hunts capacitors, made in uk.
CAP D.C.
RED: RES 32uF 275v
max ripple 250MA
YELLOW 16uF 275v
GREEN 25uF 25v
Can Negative

N Y1 KD851H ... but the H 'could' be II, as it's got a scratch across
the last letter(s)

--------------------------------------------------
From: "Vicki W" <vicert...@gmail.com>

Sent: Thursday, May 21, 2015 12:21 AM
To: <notti...@googlegroups.com>
Subject: Re: [Nottinghack] Re: 2 valve amp in record player, humming since
moving home

>> From: "Vicki W" <vicert...@gmail.com <javascript:>>

>> Sent: Friday, May 15, 2015 5:28 PM

>> To: <notti...@googlegroups.com <javascript:>>

>> > email to nottinghack...@googlegroups.com <javascript:>.

>> > To post to this group, send email to notti...@googlegroups.com

>> <javascript:>.

[Pat McDonald]

Just don't damage the board taking it out? I suppose low temperatures needed with an old board. You best replace all, but maybe you can salvage the can or if not build one. What dimensions how big this thing or a picture?

[Gazz]

No pcb type board on this amp, just a piece of bent metal with a couple of
holes punched in it for the valve sockets and condenser to poke through,
then wires to link the relevent pins,

it really is a very simple thing, just old components that are 20 times
larger than modern ones, so i guess i can gut the old condenser can, and
stick some modern capacitors inside it, but i wonder if they would be
polarised electrolytic ones, or other types.

--------------------------------------------------
From: "Pat McDonald" <thisispat...@gmail.com>
Sent: Saturday, May 23, 2015 1:13 AM

To: <notti...@googlegroups.com>
Subject: Re: [Nottinghack] Re: 2 valve amp in record player, humming since
moving home

[Pat McDonald]

I would have thought you didn't have much choice except to use electrolytic types for the higher 275V types. You might well have to choose 400V rated components rather than 275V. They should still do the job, get datasheets to check riipple rejection.

You could use a tantalum bead capacitor for the one rated at 24V. Smaller than an electrolytic.

It is very unlikely you will find non-polarized capacitors at these values. Just be careful all the cathodes are joined to case (more negative side of each, got a "-" minus sign on electrolytics) and the more positive side goes to each separate signal pin.

[Gazz]

Going to bring my GF and the record player to the space tonight, hopefully i
can find some suitable caps to use, and re-wire the amp properly,

but i was wondering if anyone who knows these simple valve amps/record
players would be in the space tonight to give me some help if needed,

--------------------------------------------------
From: "Pat McDonald" <thisispat...@gmail.com>

Sent: Saturday, May 23, 2015 7:54 PM

To: <notti...@googlegroups.com>
Subject: Re: [Nottinghack] Re: 2 valve amp in record player, humming since
moving home