A well priced valve amp kit?

[TrevorM6TSE]

Hi All,

I'm looking at building a cost effective stereo valve amplifier for use in the living room. I don't need buckets of power, so a nice simple output set like two EL84's per channel would be perfect.

I've looked at various circuits, but then it can be hard to get everything matched and get the transformers etc, so thought about just buying a kit to build. The thing that always gets me is just how much they are! They seem hopelessly over priced and are very much pointed at the audiophiles.

Does anyone know of a good kit?

All the best,

Trev

[percival007]

Hello Trev,

I would use a Mullard Circuit

http://www.r-type.org/articles/art-003e.htm

and buy the Transformers second hand from ebay. You will (If you're like me) probably have all the resistors and capacitors already in your workshop.

This is what I did when I made my first 3-3. The most expensive thing for me was the case but you don't have to go mad. I seem to remember a fellow forum member used an old biscuit tin with a lick of paint to very good effect!

As you mention, kits seem to be very expensive.

All the best and keep us posted on your progress.

James.

[Ed_Dinning]

Hi Trev, the book from which the 5-10 was taken, a Mullard publication, is readily available and may be down-loadable. It has a variety of designs in it using modern valves at powers from 3 to 20 watts as well as a variety of pre-amps that may be necessary depending on your signal sources.
Transformers for these amps are usually available on the web, prices should not be too high if you do not go for audiophool types; you can even wind your own.
Chassis production is not so difficult and could simply be a flat plate with sides/ends attached later, or fitted into a cabinet.


Ed

[Radio Wrangler]

There are websites crammed with circuits for guitar amplifiers. If you don't drive them into the end-stops all the time, they can sound quite good, though somewhat valvey.

The low distortion classic jobs like the Leaks etc used some feedback to get their distortion down to the claimed (and delivered) 0.1 percent. The problem lies in having enough feedback to get a worthwhile improvement, while still having a stable amplifier. The spoiler was the output transformer, and artful winding plans were used to try to minimise phase shift at higher frequencies. Unless you chance upon a transformer made for one of these designs, then you're going to be limited to a design with a smaller amount of feedback. Of course if any transformer rears its head on an auction site, described as ex-Leak, Quad or Radford, then the clamour amongst the phools will push the price through the roof.

EL84s have a reputation (earned in my experience) for not having long, happy lives, even the posh brands back in their heyday, and there are somewhat crappy recently made ones on the market. Again the loonies in their quest for anything thermionic with a preferred logo on it have distorted the market.

You might want to think of something with, say, a pair of 6V6s rather than the EL84s. These seem to only have guitarists chasing after them and the prices haven't gone quite so silly. Also 6V6s seem to last well and produce a pleasant sound. A number of corners were definitely cut in the design of the EL84 to get it into a small envelope. Unless you are being pressed for small size at all costs, then they are a valve worth avoiding.

Building an affordable valve amp nowadays is all about surveying what parts are available and affordable. There's no rocket science in a good output transformer, low-hysteresis transformer iron laminations are still made, copper wire is still obtainable, and with tough varnish. Bobbins are less available and you'd probably have to cut your own fish paper to sized strips. The real lack for a good finished unit is vacuum impregnation.

I used to work in a firm with its own transformer shop, and I could design and wind a unit myself and get it run through the vac impreg line. Scrap lams and bobbins were available. I designed and built a couple of very different valve amps and a couple of very different transistor ones around 1980. I measured the living daylights out of them, listened and got the opinions of friends. In the end, one went in the living room, where it still resides, and the others got boiled down for the bits. They weren't terribly different to the ear, but a choice was made and the MOSFET amplifier is still going well 32 years later. A small production run of them was made. I wonder where they all are now?

If you're doing a valve amp nowadays, then you're doing it to be different or for the industrial archeology of it all. It's interesting to try one to see what it's like, but it's one of those things where the journey is as much fun as the arrival.

Have fun,
David

[SeanStevens]

Ian and I have thought of making an amp out of TV output valves, as they are plentiful and powerful.

The only drawback is the heater voltage - but that is not impossible to get around.

SEAN

[G6Tanuki]

EL84s are rather overrated (both in terms of their power-handling capacity and from the audiophile 'the valve to use' perspective).

Look at the 6BW6 - essentially it's a 6V6 in a B9 glass envelope. One in single-ended class-A will give 5 watts or so; a pair of them in class-AB1 push-pull will give you 25+ watts.

[Radio_Dave]

Whenever I've looked into making a valve amplifier it's always the cost of the transformers (even second hand) which spoils my plans.

I recently found this 17watt ultralinear "budget amp" design using cheap EL36 output valves and equally cheap (< £10) 100V line output transformers. Current consumption is only 6.5A, so I reckon a couple or salvaged radio transformers could be used to make monoblocks

Having said that, I'm no expert and others may find problems with it. The circuit and description is here http://www.vk6fh.com/vk6fh/ECONOMICA...0AMPLIFIER.htm

David

[GrimJosef]

As others have said, in the end it's always the price of the iron (transformers) which determines the cost of self-build amps, assuming you don't charge the project for your labour at a market rate of course . And in the end what you'll have to pay will reflect the level of performance that you want. A while back there was a thread describing some home-brewed Mullard 3-3s which brought a great deal of pleasure to their owners for very reasonable costs if I remember rightly.

Beyond that, the further you go the harder it gets (see Radio Wrangler's comments about transformers and feedback stability) and the more it will cost. People who wind transformers have to pay taxes, pension costs, business rates etc as well as the rapidly growing cost of the metals themselves and these all add up. Back in the good old days production volumes were large enough for at least the overheads to be spread across a lot of trannies. But the market now is relatively small. That said transformer kits are still available. VVT do a range http://www.vvttransformers.co.uk/valve_tx_sets.htm for example. Basic component costs are cheaper in the USA (see Edcor for example http://www.edcorusa.com/c/66/gxppseries). But don't forget the shipping costs (iron and copper are heavy) and the import duty.

Cheers,

GJ

[Diabolical Artificer]

A kit will cost you more but you can probably make a valve amp in a weekend. If you want to learn more and are patient it's possible to save money and get decent transformers on eBay etc. As others have said the main cost is the OP transformers. But I picked up a pair of new VVT OP TX's suitable for a Mullard 5 -10 for £30, the chap threw in four Russian EL84 type valves for free.

I agree with other posters about the EL84, I have detailed plans using TV valves for instance that won't cost the earth or others using the 6V6/6L6 valves. Why not check out Tricomps 2C34 amp. I'm in the process of building one. If its your first build I'd really recommend the Mullard 3-3, it's a brilliant amp and there's lots of home builds here to look at.

In summary, a kit = quick and expensive. Making your own, you'll learn a lot more, cheaper. Lastly chassis. I used a top of a VCR for the metal top with some wooden sides for my 5-10 project chassis.

Good luck,
Andy.

[Refugee]

I was looking into testing off the shelf transformers.
The TV valve audio amplifiers often use mains transformers with dual 110V primaries in the outputs.
I have been wondering about using small transformers and low power valves in push pull to get about 3W for late evening listening.
The smaller pentodes are less of a problem when it comes to the price pushers.

I have used VVT for transformers, good workman like stuff reasonably priced too. I have also used Luhndal, pricey but awfully good.

[martiR2R]

Trev - I agree with everyone that trans are the biggest problem but as far as valves are concerned have you considered ECL82's, I have a nice old amp with these, around 7/8W per channel, ample for easy listening (I have the schematic if your interested). Also the later ECL86 - the Valve Museum site has a few useful designs.

Martin

[dominicbeesley]

This guy supplies stuff from Danbury Electronics. Not super cheap though! http://livinginthepast-audioweb.co.u....php?p=xfrmrpp

Other option is to try rolling your own transformers....I've made ones for TV frame output and med-fi audio by repurposing or rewinding transformers I've found. A good source is often old fashioned switch gear from factories where there are quite often a good selection of chokes and transformers to be had that can be bashed apart and rewound.

[GrimJosef]

ECL82s are still affordable but ECL86s were used in a few guitar amps and, I think, weren't made in enormous numbers. So the price of these is now rising.

The exact scheme for winding a pretty good output transformer - the one for the Williamson amplifier - was published in Williamson's original Wireless World article. Back then it was quite common for self-builders to wind their own transformers. Once you've acquired the materials, completed the windings, assembled the laminations and made a tidy job of the connections I think £50-100 will start to seem like a very reasonable price for a transformer .

Cheers,

GJ

[valveaudio]

Hi Trev

Not really a kit supplier but they have most of the hardware you might need.
www.bluebellaudio.com/
There is also another supplier, the name escapes me at the moment, but I will try to find them.

Trevor

[valveaudio]

Found it!

www.ampmaker.com/store/home.php

Trevor

[ThePillenwerfer]

Don't forget those transformers RS do: http://uk.rs-online.com/web/p/audio-...rmers/2106475/ For non-account holders Vintage Parts have them, though are currently out-of-stock: http://markhindes.easywebstore.co.uk...rs_B221QH.aspx

- Joe

[rharness]

Hi, I've made an amp fpr guitar maybe 15 watts which you could double up. It uses a pair of 6v6gt's. Basis was a KB30 radio chassis, new caps and resistors, best quality fitted on tag board and 100v line output transformer (about £15). Circuit was a Fender 5c3 off internet. Cost for everything about £120, which was a lot cheaper than the real thing. Wherever possible I used old parts.

[Ed_Dinning]

Hi Trev , I've just remembered "The LOLA", it was described on this forum a year or so ago and used 6V6's. It looked pretty good for Hi-Fi as opposed to instrumental use
Note that for Hi Fi use a transformer using Unisil GOSS lams will give better results than one using ordinary Stalloy lams.

Ed

[valveaudio]

Trev

Good range of transformers here
www.vvttransformers.co.uk/

Trevor