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Old 6th July 2012, 11:51 AM   #1
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Default Suggestions for upgrading my first tube amp!

Hi all
I'm assuming that there's a lot of knowledge flowing through this forum, so was wondering if anyone wouldn't mind musing over my first tube amp purchase?

UK 6n9p EL34-B + 5z3p Class A Tube valve amplifier amp 13W x2

UK 6n9p EL34-B + 5z3p Class A Tube valve amplifier amp 13W x2 by DHL EMS 240V | eBay

This is very much a budget-orientated purchase, but hopefully should live up to my initial (low to medium)expectations.

I choose this as it appears to have point-to-point wiring & a pretty good variety of tubes included. I also like this 'kit-style' model, as so many of these cheap chinese amps have rather 'busy' case styling, which isn't to my taste. Once this arives, I hope to run my KEF Cresta 3's through it. I will be using my old ARCAM Delta 7SE CD Player.

So, what do all you tube-buffs think of this beginners setup?

What relatively simply/cheap(ish) upgrades would be available to me? What commonly available specifc model/brands of replacement tubes could you recommed? My limited knowledge/ reading into this subject also advises volume pot upgrades... any to recommed?

All input welcomed

Regards

Andrew
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Old 6th July 2012, 01:08 PM   #2
DF96 is offline DF96  England
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Unlikely to get 13W from an SE EL34, unless they are Chinese watts. The missing bottom panel almost certainly means that this unit does not meet the requirements of the Low Voltage Directive so it would be illegal to sell in the EU, but then it doesn't appear to have a CE sticker so it doesn't claim to be legal. Make sure the amp, especially the underneath, is completely inaccessible to any young children in your house.

The OPTs look a bit small so it might have trouble with deep bass. Probably an SRPP (Chinese love SRPP!) with pentode-connected output; in effect a slightly higher power version of a 1950's radio set audio stage. At least they haven't wasted money on styling. The missing bottom and twisted (rather than screened) wiring could mean some problems with hum and interference pickup, but you may be OK. At this price level a thermionic rectifier is merely a fashion statement to boost sales.

With low expectations you are unlikely to be disappointed.
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Old 7th July 2012, 04:04 AM   #3
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Looks pretty cool and a good base to improve upon. I would replace the capacitors with some better Elna Silmics and get some good vishay metal film resistors for upgrades. I'm a tube nube myself and I am working on an oatley electronics headphone tube amp. It is actually a hybrid amp, but I am doing these upgrades on this kit, and putting some vintage 1988 Russian LEDs on it for coolness! I am going to put it in a cast aluminum enclosure and have RCA inputs as well as mini jack in and out. ALPS for voluume. I hope it works...
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Old 7th July 2012, 06:11 AM   #4
tomchr is offline tomchr  United States
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I agree with DF96's observations. The output transformer does not look like it'll be able to handle 13 W. Never mind getting 13 W from a single-ended EL34 in the first place. An OPT that can handle 13 W at 25 Hz is generally around 3.5x4 inch footprint and probably 4~5" tall. Taller than the tubes.

I suggest looking at George's (tubelab) Tubelab SE or Tubelab SSE. He sells board for these, so they're pretty easy to put together. For less money than you'll spend on that eBay amp, you can have something that performs well. Output transformers from Edcor, power tranny from Antek (or Edcor if they have anything suitable), board from tubelab.com, tubes from eBay or any of the on-line vendors.

Sorry to burst your bubble, but I'd rather send you off on the path to possible success than the one to (nearly) guaranteed failure.

If you've already hit the Buy button, then I'd look at upgrading the OPTs and replacing the anonymous looking (silver) electrolytic capacitor with something better (Nichicon Muze KZ for electrolytics or a good polypropylene cap). I'm guessing it's the cathode bypass cap.

~Tom
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Last edited by tomchr; 7th July 2012 at 06:16 AM.
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Old 7th July 2012, 08:55 AM   #5
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Thanks for the replies, so far!
I was never expecting this amp to be the dogs-danglies out of the box, haha.
I will look into upgrading the OPT... any specific UK-compatible 240v models anyone could recommend on a budget?
The capacitor upgrades should be cheap & easy
Cheers all!
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Old 7th July 2012, 01:08 PM   #6
DF96 is offline DF96  England
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In the UK try VVT or Danbury (via Living in the Past) for transformers. If money is no object then Sowter.
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Old 7th July 2012, 11:54 PM   #7
tomchr is offline tomchr  United States
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Quote:
Originally Posted by TUBEHEAD79 View Post
I will look into upgrading the OPT... any specific UK-compatible 240v models anyone could recommend on a budget?
OPT = Output transformer. It's specific to the tube not the mains voltage.

In the US, Edcor provides good bang for the buck. I'm sure they ship internationally, but the cost of shipping may make that a non-starter.

~Tom
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Old 8th July 2012, 01:00 AM   #8
12E1 is offline 12E1  United Kingdom
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Also Hammond are an option for transformers - available from sellers in the UK and in Europe (plus US & Canada of course).
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Old 8th July 2012, 09:48 AM   #9
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It all depends what you mean by upgrade. If you don't have the knowledge to change the circuit and swap in new parts and values you are pretty limited.

If you were to do a root and branch modification to the whole amp you might consider using 300b outputs. However, I have no idea what the actual HT voltage is so this may not be practical. It appears to say 300v and that's too low unless you changed the mains transformer. You'd need to add some kind of filament transformer for the 300bs as well, and probably change the rectifier. Not impossible. You could use decent 6SN7 inputs, and there are a number of published circuits for that. For a different mains transformer contact Philip at Bluebell Audio - he's very helpful and knows tube circuits. The 300BX is the Hammond mains transformer for 300b SE amps.

http://www.bluebellaudio.com/

If you used 300b outputs the output transformers would need to be gapped for at least 60mA

But if you wanted a more sophisticated amp, it would have been better to start with a different model in the first place.

This amp will give you a taste of tube sound, but it's basically a taster.

Last edited by andyjevans; 8th July 2012 at 10:10 AM.
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