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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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14th Jan 2021, 8:21 am | #41 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,657
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Re: Selmer Bassmaster 50 - mains transformer
Good to hear your making progress. Noticed a mistake, the red wire (HT?) off the valve base, top left is going to what looks like a mains fuse,this then goes straight on to a big cap. 1) if it is 400v ish HT it should go to the bottom tag on the valve holder,anyone changing a fuse could get a belt. 2) What's the point in the wire/connection then going off to the cap? It's not fused.
Also noticed what looks like a zener,or resistor, top of tag board flopping about. Sorry,there's your,your caps in the smoothing section have long leads and as Dave Jones says are "flapping around in the breeze". Big electrolytic aps have mass and as such should be secured, every bump or knock will stress the solder joint leading to potential failure. Looking again at the fuse I can see another fuse holder, looks a bodge of two fuse holders, hard to see what's going on, there's wires all over the shop, keep wires as short as poss,same colour for same part of circuit, EG red for HT, black for ground etc & keep your work neat and tidy. Remember,someone else will probably work on this after you, if they're a good tech & your work is good, it makes it easier for them & you'll get praise & not a roasting. Hope this comes over as constructive criticism rather than a personality execution. Andy
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15th Jan 2021, 4:29 pm | #42 |
Triode
Join Date: Jan 2021
Location: London, UK.
Posts: 12
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Re: Selmer Bassmaster 50 - mains transformer
Thanks Andy, I think I might survive! The issue with the red wire is an optical illusion, actually it is coming off the HT fuse above the mains fuse, going to the big capacitor, so fortunately no danger there. The amp originally had no HT fuse. I put it there so that I wouldn’t have to make a new hole in the chassis, and therefore keep things more original. However, you are right that it doesn’t look very neat, and also you would have to pull out the chassis to change it, so I am going to move it to a new holder in the back panel. The “flopping about” resistor you identify is me experimenting with values to get the bias for the output valves to the correct value, so will be replaced on a more permanent basis.
I got hold of a new meter, which pretty much agrees with my old meter within 2%. This shows that our mains voltage is around 230v, which might give some explanation why the heater voltages are a bit low. With the correct biasing, the HT voltage is now showing at 362v. The voltage at the secondary is showing as 281v AC. The open circuit secondary voltage with the valves out was 300v – is this a reasonable drop under load? |
15th Jan 2021, 4:52 pm | #43 | |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Selmer Bassmaster 50 - mains transformer
Quote:
PS. Glad you have it going again.
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15th Jan 2021, 11:35 pm | #44 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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Re: Selmer Bassmaster 50 - mains transformer
Glad you got it sorted. I've serviced a couple of Treble and Bass, nice amps and they're much more appreciated these days.
I'm puzzled by the your 'low' mains voltage though, I'm not doubting your meter readings but when I lived in London (south) I dont remember it ever being lower than 240/245V? It's 250V down here, sometimes creeping up to 253V? |
16th Jan 2021, 6:27 pm | #45 |
Triode
Join Date: Jan 2021
Location: London, UK.
Posts: 12
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Re: Selmer Bassmaster 50 - mains transformer
Thanks Alan, I tried the test in my admittedly cold shed, with the chassis open on the bench, and the transformer got no more than warm after over an hour, so I am reassured.
Itam, I guess the voltage one gets at the socket is mainly dependent on the equipment in the local substation. I am usually getting around 231, up to 234v. Maybe our substation is equipped with the 230v standard in mind, or is usually overloaded! |
21st Jan 2021, 4:40 pm | #46 | |
Heptode
Join Date: Oct 2019
Location: Täby, Sweden
Posts: 702
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Re: Selmer Bassmaster 50 - mains transformer
Quote:
Manufacturers usually allow a further margin of safety and, if the voltage does occasionally fall outside these limits, there should be no adverse effect on your appliances. In the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts. Voltage changes So your 253 is a bit 'hot'. |
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