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Old 18th Oct 2012, 11:37 pm   #21
MrElectronicman
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Default Re: A well priced valve amp kit?

If you already have some of the parts, it's really a lot of fun to build your own amp.

I am in the process of building a stereo amp using 6BW6's single ended. driven by an ECC82. I also decided to include an active tone control using a Baxandall circuit using ECC83's. The 6BW6's are quite simple to use and are much cheaper to buy than EL84's.

Since I did not have any suitable audio output transformers I got some Hammond 125 series which are not so expensive and they are not rated as Hi-Fi , but since I cannot hear much above 10Khz these days it does not matter.

I already had a power transformer, which is some what under powered for the job, but even so with at amp at full power it's very loud and has very little distortion. The amp was constructed using an old chassis I had lying around so it is not very elegant, but it works.

My next project will be to use the 6BW6's in push pull, but I expect that I may not be able to use it at anywhere near full power.
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Old 19th Oct 2012, 12:39 am   #22
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Default Re: A well priced valve amp kit?

This lot have a good few reasonably priced valve amp kits, they're in Hong Kong though - that may or may not be a problem..... postage can be surprisingly reasonable.

http://www.analogmetric.com/index.php

Cheers,
Steve.
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Old 19th Oct 2012, 11:12 am   #23
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Default Re: A well priced valve amp kit?

If you're doing it on the cheap rthe other thing to think about is using PCL82/6 valves. These telly valves are a lot cheaper but more prone to hum. Rigging up a DC supply isn't too difficult though...
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Old 20th Oct 2012, 8:10 am   #24
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Default Re: A well priced valve amp kit?

Wow,

Thanks SO much everyone for all the replies! It's quite an emotive subject isn't it?

I've got quite a few valves of various types and some discrete components, but it's always the transformers that worry me.

I did toy with the idea of 100v line transformers, but wasn't sure if it would work.

I also like the idea of an old stereogram. I think I may look into this further. I normally don't like butchering old kit, but at the end of the day most old stereograms are not loved or wanted so if at least part of them lives on it must be good.

Freecycle for me I think!
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Old 1st Feb 2013, 12:11 am   #25
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Default Re: A well priced valve amp kit?

A further option for PP is to use power toroids (RS?) for output iron 110-0-110V, The main thing is to balance the current in the two windings. I have been running a stereo amp with 2x EL34 O/P stages with CCSs for over a year, admittedly it is only used for a few hours every couple of weeks but the balance is still good. Sound is excellent, for more info search on diy Audio site. The Toroids need to be rated about 5x the wanted power output, For a PP 5W amp 25VA toroids would be fine. Choose toroid secondary voltage according to your speaker impedance.
Power toroids are cheap and the frequency response will surprise you!!!
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Old 1st Feb 2013, 6:34 am   #26
Anthony Thomas
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Default Re: A well priced valve amp kit?

Quote:
Originally Posted by trickytrev View Post
Wow,

Thanks SO much everyone for all the replies! It's quite an emotive subject isn't it?

I've got quite a few valves of various types and some discrete components, but it's always the transformers that worry me.

I did toy with the idea of 100v line transformers, but wasn't sure if it would work.

I also like the idea of an old stereogram. I think I may look into this further. I normally don't like butchering old kit, but at the end of the day most old stereograms are not loved or wanted so if at least part of them lives on it must be good.

Freecycle for me I think!
Regarding transformers, for a single ended output transformer have you ever considered using a mains transformer and re stacking the laminations and inserting paper as an air gap?

Not my idea but one I might try one day; I always keep old transformer laminations just in case they may be re-usable one day.

Tony
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Old 1st Feb 2013, 6:54 am   #27
Ed_Dinning
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Default Re: A well priced valve amp kit?

Hi Tony, mains transformer lams are usually stalloy. This has quite a sharp "knee" on the saturation curve and so will give some distortion, this type of lam is better for instrument use rather than hi fi. Unisil, GOSS, lams are more expensive but have a much smoother saturation curve and are generally used for the better op transformers.
Typically stalloy is run at about 1T for mains transformers, but can be pushed harder if losses are not a problem. For op use it should be run at about 0.6T.
Unisil will run at 1.5T for mains use, say 0.8T for an op.
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Old 1st Feb 2013, 10:03 am   #28
ColinTheAmpMan1
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Default Re: A well priced valve amp kit?

Hi,

I wouldn't use a guitar amp design for "hi-fi" if I could avoid it. Guitar amps are voiced rather peculiarly and don't really suit other sources. Also, a hi-fi amplifier isn't the best choice for amplifying an electric guitar.

I posted some stuff on the RSC A11 14 watt amp on this forum (https://www.vintage-radio.net/forum/...t=82936&page=3).
This was originally supposed to be a hi-fi amplifier with a Baxandall tone-control setup. I have since modified it for guitar, but the original circuit could be something like you want. Sourcing power and output transformers may not be that bad. Maplin (used to) do some which might be appropriate.

Regards, Colin.
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Old 1st Feb 2013, 2:52 pm   #29
Whaam68
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Default Re: A well priced valve amp kit?

Hi

If you can pull the parts together yourself I think you could get a better amp:

George anderson at Tubelab has a number of great pcb's including the Simple PP, Simple SE & SE. I built the Simple SE with great results.
http://www.tubelab.com/

Shannon Parks over at diy tube has 8 different types of amp pcb's covering all topologies: I've built the GetSetGo with 6B4G's (probably my favourite amp) and a Clementine using 807's.
http://www.diytube.com/phpBB2/index.php

I bought transformers from Edcor & from Transcendar in the states although postage has gone up a lot lately (this was a few years ago). Also Bluebell audio in the UK are very good.

If you want to avoid the cost of output transformers you could try one of the PASS diy zen mosfet/jfet circuits? with a valve preamp. I recently built the Ampcamp 5wpch (jfet) amp from the boards on sale at Diyaudio and this held it's own against my valve amps for not much money (although currently out of stock).

http://www.diyaudio.com/store/amplif...amp-kit-1.html

regards

Mike
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Old 1st Feb 2013, 3:53 pm   #30
Alan Stepney
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Default Re: A well priced valve amp kit?

Whilst many people suggest the Mullard circuits (and they are good)
dont discount the Osram 9-12 etc.

As for parts, I have recently sold some completed home made vintage amplifiers and they fetch less than the transformers would cost, so it might be worth exploring that route.
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Old 1st Feb 2013, 11:58 pm   #31
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Default Re: A well priced valve amp kit?

Trev
You could look at this Dutch company for toriods.

http://www.toroidal-transformer.com/

Trevor
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Old 2nd Feb 2013, 3:15 pm   #32
rharness
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Default Re: A well priced valve amp kit?

Have a look at the Weber amp kits, you can select which parts to buy and you get circuit diagram and schematic to view on the site, for beginers.

http://taweber.powweb.com/store/kits_50a.htm
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Old 6th Feb 2013, 11:23 am   #33
Neil Purling
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Default Re: A well priced valve amp kit?

The audiophool can be quite ridiculous. If you were making a 3-3, like I did and insisted on a European name like Telefunken brand valves, the 3 necessary valves would be around £150.00.
I made mine with much help from Forum members: Power transformer, o/p, 50/50 smoothing can, and a Reflektor EL84 from a Rigonda.
These parts were all re-cycled via the Forum. The new parts I had to buy were the resistors & caps, plus the EF86 (Svetlana). The chassis was re-cycled from another project.
The o/p transformer was one of a pair from a old Armstrong receiver.
I have passed them on to another Forum member making a stereo 3-3, after I had Ed wind me a EL84 o/p transformer. As they were a pair it made sense not to hang onto them.
And so far I have had no problem with the used, ex-Rigonda Reflektor EL84.
They are not being ridiculously over-volted as they would in a guitar amp. I obeyed the official component values completely, and I suspect the EL84 is not run hard.
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