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Old 29th May 2015, 03:36 PM   #1
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Default Suggestion for valve amp kit

Sorry for what is probably a newbie question but please bear with me! I have always liked the sound of valve equipment and have been thinking for some time about building a valve amp. I have sufficient electronics skills and have repaired a few valve radios, but I do not have the equipment or skills to fabricate a chassis or PCBs, so I'm thinking that a kit might be the way to go. I would like the amp to be stereo and have a pre-amp stage if possible. I have noticed that some designs use at least some semiconductors which I do not object to although I am aware that the purist would consider only valves.

I have searched for a while and there seem to be a lot of different kits around. Some come from the far east via eBay and Amazon and appear to be reasonably priced but I have concerns over quality of components and therefore ultimately how they might perform, although I understand some aspects can be improved by upgrading the originally supplied components. It goes without saying that I don't want to spend my hard earned cash on a piece of junk. On the other hand, you get what you pay for, and I have seen other kits from perhaps more specialist vendors that are very expensive (i.e. in excess of 1k or as much as even 3k!) and am wondering whether it is better to save up for another year or two.

Before I decide what to buy I also have a couple of questions:

1. What is the advantage of single ended amps over push pull?
2. Since extra grids on the pentode were added so as to solve certain problems with the triode, why do some consider a triode output stage superior?
3. I understand that due to the nature of valves, valve amps have a problem with response below 100hz. Do modern valve amp designs solve this, or is this a limitation one must live with?

My total budget is around £500 (or around 700USD), although by the time import costs are considered it might as well be 500USD. Is this sufficent to build something that might be upgraded later?

Last edited by WaveyDipole; 29th May 2015 at 03:43 PM.
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Old 29th May 2015, 05:04 PM   #2
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You are going to have budget problems. Magnetics are expensive, especially SE O/P "iron". Without arguing pros and cons, this fact alone indicates build PP circuitry.

Well designed tube circuitry will be "flat" throughout the entire 20 - 20000 Hz. band. FWIW, the Harman/Kardon Citation II easily bests very many SS amps in the bass performance area.

A deep, heavy wall, commercial kitchen, aluminum baking pan makes a good low cost chassis. IMO, this is your best bet, when financial constraints are present.

What sort of speakers do you plan on using. The amount of power O/P yielded is directly tied to speaker behavior. Amps and speakers form an "organic" whole.
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Old 29th May 2015, 07:21 PM   #3
hectori is offline hectori  Chile
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I Buy and Build this kit : https://momchil.wordpress.com/2013/1...D0%B3%D1%8350/

Great for the price and the GU50 tube is a beast...
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Old 29th May 2015, 08:31 PM   #4
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Quote:
Originally Posted by hectori View Post
I Buy and Build this kit : https://momchil.wordpress.com/2013/1...D0%B3%D1%8350/

Great for the price and the GU50 tube is a beast...
It looks good hectori. Had seen it somewhere else before, near the Andes.

Saludos.
P.
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Old 29th May 2015, 09:02 PM   #5
hectori is offline hectori  Chile
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As seen on HifiChile :P i have to update the pictures, the amp is almoust ready.
Saludos!
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Old 29th May 2015, 09:51 PM   #6
tomchr is offline tomchr  Canada
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A Spud (single-tube) amplifier is a good way to get started with valve/tube amplifiers. My Novar Spud can be built for around $200 (board, components, iron) using the small Edcor XSE output transformers. If you want better performance, the Edcor CXSE transformers are incredible value for the money. With the CXSE transformers, the budget gets up to about $300. Then add chassis.

Tom
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Old 29th May 2015, 11:15 PM   #7
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I do not claim to be an expert, however:
1- Single ended triode blah blah - is a purist route, sometimes a black art, the quality of (spelt expensive) components are a key feature.
with your budget stay away.
Some argue that single ended designs sound the best, Naah!
it is a belief that started in Japan, even Tim de Paravicini of EAR, Lux, MFSL (& many more) believes single-ended is over-rated at best.
2- No problems with bass output, don't worry! Bass players love valve amps (so I've been told)
3- with your budget, try to pickup an Edison 12 or similar from eBay (google it) and modify it.
it is a simple EL84 push-pull poweramp of some 12 watts.
If you modify it to manual bias, upgrade the powersupply (better caps and a choke) you get over 15 Watts clean from it.
It has decent transformers, and with a little modification (bypass the first tube) you could feed it a DAC signal direct (& use a digital volume).
I have one at my office and it sounds great through my Sonus Faber Concerto's.
As mentioned earlier in some reply, you need the right speakers too.
Good luck.

Last edited by KenTajalli; 29th May 2015 at 11:18 PM.
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Old 31st May 2015, 07:08 AM   #8
DieterK is offline DieterK  Germany
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When you will Play with a single Endet Amp you need good Speakers with a high Intensyty bigger than 90dB/W and relativly linear resistence over the Frequency. With your budget by an used Push-Pull Power-Amp like the Dynavox VR-70 or similar and modify it. It is a good base to hear music and learning something about Tube-Amps. I spend <500$ for the complete Amp incl. Some modifikationes. Today I'm on the way to make my own Amp-Design without compromise and this means also to spend more than 2k$ for the technic. Really good Amplifiers cost a lot. So my Opinion: Start like me with an ready China-Amp and learn to modify it.
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Old 1st June 2015, 11:12 AM   #9
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A few interesting suggestions being proposed even all the way from Chile!. I've sent the vendor an e-mail asking for the price of the GU50. I am intrigued also by both the spud and the Edison 12 and I noticed while Googling this that there is also an Edison 60 as well and it might be possible to source one within the UK, which I am seeking to confirm and get some idea of price. I haven't had a chance to do an eBay search yet though.

My speakers are Boston A26s and have a sensitivity of 89db, so just a shade short of the 90db that is recommended. Would they still be suitable?

Regarding the Dynavox, I can see they are listed on Amazon.de so are also an interesting option. Again, there are other options such as the Dynavox 20 which is slightly more expensive but the listing does not appear to state which valves it is using. I must also admit that I don't like the appearance of the capacitors protruding halfway through the chassis on these two amps. Another amplifier that came up as an option was the GemTune which also has 4.5 stars and I think is nicer in appearance, but is it as good as the Dynavox?

Last edited by WaveyDipole; 1st June 2015 at 11:20 AM.
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Old 1st June 2015, 12:41 PM   #10
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If you really don't want to make a chassis, you could do a lot worse than something like this: DIYTube Dynaco ST35 Tube DIY Amp Kit - NEW REV. E! Great for iPod
It is a well tested push/pull design that will have plenty of power to drive your speakers to respectable volume.
If you could find someone to help with the metalwork, other options open up like the SPP from tubelab.com or something similar.

You certainly don't need to spend $1k+ to get something that'll sound great.

Good luck.
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