Millenium 4-20 (Maplin Electronics)

[Dave Ed]

I think I'll conclude by saying that from a standpoint of cost you can still get up and running for not a lot. I think the original kits back then cost £50 for a power supply and 2x£150 for the amps=£350 for a stereo unit. A copy of Hi-Fi World in 1994 was £2, up to £3.80 last time I looked so nearly a 50% jump, I've managed to get this far for £390 approx. a £12.5% hike!
Some parts that were used in the original kits Maplin's simply do not stock anymore such as the pcb's (that is asking a lot), polystyrene capacitors-I have substituted their polyprops for these-and I understand that the audio caps. they carry are maybe not of the quality of the originals-but they still do output t/x's for el 34's and some high voltage power supply caps(don't hold me to that it's been 4 months since I checked).
I was amazed when music came out of the right end of it-and it holds up very well compared with my kel84 except the top end-but, as you've all pointed out there are so many variables alone in system matching and interaction that to pin the reason for this 'fault' to the amp would be unfair when those that have commented on the sound of their own el34 amps all find the sound opposite to me. I'm certainly not complaining- it's just an honest observation of what I'm hearing.
Right, where's that soldering iron.............!

[Mike H]

Oh yes absolutely, certainly for a first timer it's quite staggering.

Actually Maplin's current LCR polyprops are much better than what was used originally, it's just that there's better again!

Re the cct boards, I'm reminded that shortly after the kit was DIS'ed (incidentally one story I was told is that the DIS'ing of it included a health and safety issue, the point being that both this and the Velleman K1040, also a complete kit, were not fully enclosed, that is hot valves exposed for any unwary young kiddies to grab hold of by mistake and that kind of thing)

Anyway, Maplin still had some boards left over and one guy emailed me about how to get them off Maplin, but they wouldn't give 'em to him, there was some ruling that everything had to be destroyed

Before that 'leftovers' would've gone to the nearest shop for the 'bargains bin'

Forgot to mention that re the 'poor top-end', I think this is to do with a deliberate roll-off in the original Mullard design, for the simple reason that back in the '50's audio material hardly ever went beyond about 5 kHz, anything above that was just noise... hence the plethora of complex filters and suchlike added to pre-amps...

Well if as and when I can get together another prototype I'll let you know!

Photos as well, try to get back on topic ...

[Richard]

Originally Posted by Mike H

Forgot to mention that re the 'poor top-end', I think this is to do with a deliberate roll-off in the original Mullard design, for the simple reason that back in the '50's audio material hardly ever went beyond about 5 kHz, anything above that was just noise... hence the plethora of complex filters and suchlike added to pre-amps...

Mike,

I'm not sure I follow this (sorry if I misunderstand your meaning ). The 5-20 response and power bandwidth was greater than most amps of the period and more than many modern designs even aim for.

From my reading of Mullard's book, it was modestly called 5-20 and Twenty Watt Amplifier based on that being the audio power bandwidth.

Spec was,
2Hz - 100KHz +/-1dB 1W response and
30Hz - 20KHz +/-0.5dB 20W power bandwidth.

Maximum output was 27W over much of the middle bandwidth and I found these figures checking mine without problem (built with good transformers).



Rich

[Mike H]

Thanks for that ~ you have the better of me, I don't have that info ~ or I should have but not sure where it is at the mo.

Dunno what it is then!

'Tis a bit wide innit? True tho that according to one EL34 app data sheet the same o/p stage should do 30-something Watts, given sufficient HT

How long the EL34's will last like that is another matter of course

[Richard]

Originally Posted by Mike H

Thanks for that ~ you have the better of me, I don't have that info ~ or I should have but not sure where it is at the mo.

Dunno what it is then!

'Tis a bit wide innit? True tho that according to one EL34 app data sheet the same o/p stage should do 30-something Watts, given sufficient HT

How long the EL34's will last like that is another matter of course

Mike,

Perhaps I've made a bit of a gaff here . Are you this Mike H (Holmes) or another one?

[Ianm2]

he' the same one rich, we are in exalted company

v comprehensive specs, too.this and the pre was a very well thought out and planned/executed project, attention to detail in the article and in the circuit

[Mike H]

I am indeed one and the same, why is there a problem?


Oh I see what you mean, if not it would seem odd

Maybe it's just me being super-fussy, just if I were to do it again I'd do it differently. Not had a Millennium since making the prototype, which 'disappeared' soon after I produced it. Never saw it again. Had Mullard valves in it as well.

Just that some commentators accuse it of having poor treble, whereas I've also been told it's too bright! Maybe depends on their speakers or ears. Only one way to find out, actually make one. That's my next project, but still have to make a chassis first.

[Richard]

Thanks Mike, no problem and glad you're not an imposter . I just thought some of your comments were a bit hazy hence my email to you to check. If you've not had a 4-20 for 14 years that explains it

Rich

[Mike H]

Rich was a bit worried who's this bloke rabbiting on, seemingly not knowing what he's on about...

Should explain had a bit of a clear out while ago prior to a bit of a redecorating session, had piles of paper and magazines >10 yrs old taking up too much space and nowhere left to put it, it had to go. My mistake for assuming no-one is going to be using the original instructions ever again! I'd scanned the Newton articles, forgot the Millennium

[ian_r]

I have scans of the relevant pages (including the follow up) + powerpoint slides of the PCB layouts (with the error corrected) - if anyone wants them pm me and I'll dig them out.

Ian