Mullard 5-20

[david counter]

maybe because of the recent interest I have the burgeoning idea to build a 5-20
can anybody point me in the direction of an easy to understand circuit that's not too difficult for an idiot like me

[Allen]

I have the Mullard book if you want to borrow it.

[alnewall]

http://www.lundahl.se/pdfs/claus_byr...fier_30wpp.pdf

Its in this pdf file along with some good reading. A web search will reveal some variants.

[david counter]

thanks guys

[John Caswell]

Hi Dave,
The beauty of the Mullard book is that it gives all details of how to build it incl. chassis work, so you could take the drawings to a local tin basher and get two professionally made chassis etc.
If you decide to go this route get the best O/P txs you can afford as they are the final arbiter, but you may have to change the feedback R/C slightly to accomodate modern Txs.
When I built them I was able to buy the Partridge C core txs, P6878 rings a bell, but at what cost to my pocket! Two were about 3 months spare cash.
Results were well worth it though.
I still rate it as one of the best U/L applications of EL34s.

Regards

John aka Dr john

[ian_r]

Also worthwhile looking at the old Maplin magazines for the Millenium amp which is very close to the 5-20 design. Its easy to modify the front end to that on the shown on the lundahl site pdf. I have scans and PowerPoint overlay files for the PCBs for this if you want them. I was surprised how good it sounded after changing the front end.

[david counter]

If I understand it correctly the Kel 34 had a version of the 5-20, is this worth looking at with a view to building a hard wired one

[alnewall]

Ian R.

I'd be interested in any info on the Millenium.
I've got one without tube rectification (4-20). Sounds quite nice, although it needs better transformers. But is it worth the expense?

[hifienthusiast]

Originally Posted by John Caswell

When I built them I was able to buy the Partridge C core txs, P6878 rings a bell, but at what cost to my pocket! Two were about 3 months spare cash.
Results were well worth it though.
I still rate it as one of the best U/L applications of EL34s.

Regards

John aka Dr john

Vintage Partridge transformers still worth a lot of money even nowadays, especially in internet auctions, but perhaps not as much as 3 months spare cash!

Hon

[Richard]

Hi All,

I'd build them standard circuit first. Don't imagine Mullard didnt know what they were doing, you'll be surprised. Just because a modern designer changes things it doesn't mean it's an improvement.

I found certain things do improve them a little. With good OPTXs and supply they can go lower in the bass and the mid seems to benefit also. I imagine bass was left to roll off due to wobbly vinyl sources but with CD and big speakers you'll be surprised how good it can be.

By all means digest all sources of the circuit and builds and mods, The Maplin version was very good value but will not be the best due to cheaper TXs and lower power supply.

Rich