okay I've found some Mustards on ebay, 0.1uf. that's what is on the top half, which doesnt seem to be as molested as the bottom half. The bottom has had 0.047 Arco caps, should I stick with 0.1 like the original? Also what brand would be recommended for the electros? I normally use Elna Silmic but not sure if something else would be more suitable. Running it set to 4 when my speakers are 8 ohm will be okay? I do have some 4 ohm Acoustic Research AR11 but I thought they would need a lot more power since they're only 86db efficiency.
HMV valve amplifier
- Thread starter Budney
- Start date
wd40addict
pfm Member
Back on the day quality speakers were 15-16 Ohms and lesser units 3-4. This meant less copper needed in the cheaper units, but potentially more loss on the cables. 8 Ohm arrived later as a compromise.
Barrymagrec
pfm Member
15 ohm speakers fell out of fashion partly because early semiconductors couldn`t support the rail voltage required for high power into 15 ohms.
snowman_al
pfm Member
Personally I would run it up on the variac and see what that brings before swapping out parts.
It will not do any harm running 8 ohm speakers on either the 4 or 16 ohm setting, or 4 ohm speakers on the 16 ohm setting for that matter. Valve amps have a great tolerance to output impedances, just choose the one that sounds best to you. The caveat is do not run the amp without any speakers or dummy loads connected.
Make sure the 0.1µF Mustards are 400 volt rated. I would wait until it is working before buying any.
The hole next to the hum bucker is not populated on the 'other' 557s. (Looks like it is on the 555 and 556 stereoscpoe models. And there is a lot of chassis parts sharing between models.)
Only picture I have found yet are here: http://www.levick.de/hmv.html
and 7th down the page here: https://m.review33.com/forum_msg.php?db=1&tstart=0&s=&topic=27120311101511&start=145&sort=&number=5
Scroll down further and there is a picture of the under side of a 555.
Just guessing now, but I wonder if the original unit with the extra ECC83 followed the Mullard 5-10 circuit and used a LTP (Long Tail Pair) phase splitter? Then as a cost reduction the concertina phase splitter (as yours) came into use? (At the same time the ECL86 was used on other models. The ECL86 lends itself to the concertina PS.)
F&T do all sorts of high voltage axial caps in various styles. What value/s is written on the Green Plessey caps?
It will not do any harm running 8 ohm speakers on either the 4 or 16 ohm setting, or 4 ohm speakers on the 16 ohm setting for that matter. Valve amps have a great tolerance to output impedances, just choose the one that sounds best to you. The caveat is do not run the amp without any speakers or dummy loads connected.
Make sure the 0.1µF Mustards are 400 volt rated. I would wait until it is working before buying any.
The hole next to the hum bucker is not populated on the 'other' 557s. (Looks like it is on the 555 and 556 stereoscpoe models. And there is a lot of chassis parts sharing between models.)
Only picture I have found yet are here: http://www.levick.de/hmv.html
and 7th down the page here: https://m.review33.com/forum_msg.php?db=1&tstart=0&s=&topic=27120311101511&start=145&sort=&number=5
Scroll down further and there is a picture of the under side of a 555.
Just guessing now, but I wonder if the original unit with the extra ECC83 followed the Mullard 5-10 circuit and used a LTP (Long Tail Pair) phase splitter? Then as a cost reduction the concertina phase splitter (as yours) came into use? (At the same time the ECL86 was used on other models. The ECL86 lends itself to the concertina PS.)
F&T do all sorts of high voltage axial caps in various styles. What value/s is written on the Green Plessey caps?
I admit that's going over my head a little bit, not sure what the difference in phase splitter circuits would be! I guess if there less active components in the signal path it should sound better?
I don't have access to the workshop currently so will have to wait a little while to get it on the variac with the dummy loads. The green caps are 15uf so I assume I can replace 2 of them with a single 32uf?
Didn't realise they made different versions of this amp, I might try and contact http://www.levick.de/hmv.html and see if I can get any more photos
I don't have access to the workshop currently so will have to wait a little while to get it on the variac with the dummy loads. The green caps are 15uf so I assume I can replace 2 of them with a single 32uf?
Didn't realise they made different versions of this amp, I might try and contact http://www.levick.de/hmv.html and see if I can get any more photos
okay so I finally got round to looking at this guy, brought up on the variac and all seemed okay, no magic smoke! Sadly on closer inspection one of the EL84 was cracked so have left that out. Only tested one channel at a time, but they both seem to work! one strange thing, its gets rather microphonic...? as in when I send a hot signal, I can hear it vibrating out of the amp! maybe somewhere around the transformers, when playing a sin wave its very noticable once it starts to clip. Is this normal?
Pre amp isn't working, no 6.3V coming from its rectifier so that's dead, but im very happy that both channels seem to be working okay with one set of valves. I think I may be able to notice a slight dullness to the channel that has had some caps replaced, but I couldn't really say as I can't listen in stereo right now. HT hovers around 300V.
I'm not sure what my next step is now? I guess all the electrolytics could do with being replaced, as well as any other caps have been messed with. I will replace the rectifiers with diodes as well. A friend of mine has some Mullard EL84 he said I could have, so will be able to give both channels a test when I get them. I've only used it on test loads and a crappy test speaker, but it does seem to have a rather sweet sound to it
Pre amp isn't working, no 6.3V coming from its rectifier so that's dead, but im very happy that both channels seem to be working okay with one set of valves. I think I may be able to notice a slight dullness to the channel that has had some caps replaced, but I couldn't really say as I can't listen in stereo right now. HT hovers around 300V.
I'm not sure what my next step is now? I guess all the electrolytics could do with being replaced, as well as any other caps have been messed with. I will replace the rectifiers with diodes as well. A friend of mine has some Mullard EL84 he said I could have, so will be able to give both channels a test when I get them. I've only used it on test loads and a crappy test speaker, but it does seem to have a rather sweet sound to it