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Old 19th October 2007, 03:58 PM   #1
chrisbp is offline chrisbp  United Kingdom
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Default Suggested replacements for Chinese tubes

I have recently purchased a pair of mono chinese tube amps - same as these - http://cgi.ebay.com/Pair-of-EL34-Val...QQcmdZViewItem

I have ordered a pair of Svetlana 6N1P tubes to replace the Chinese ones it came with (they wernt even a matched pair - different designs!) I would like to replace the other tubes as well.

Each amp has a 5Z4P and an EL34. Is there any point changing the 5Z4Ps - do they alter the sound much? Which equivalent tubes are there for the EL34. I have heard the KT77 is an equivalent. There is a similar model amp which uses the KT88 - is the KT88 compatible?

Cheers for any advice.

Chris
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Old 19th October 2007, 04:23 PM   #2
kevinkr is offline kevinkr  United States
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There are many different brands of EL34, currently some popular are ones from EH, JJ, the Mullard reissue from New Sensor. (May be hard to get in the EU?)

Note that JJ currently seems to be having issues with the quality of some of their power tube products. This would include the KT77.

Jim McShane would be a good person to contact about alternatives.

I wouldn't swap in a KT88 without knowing a lot more about the amplifier design.
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Old 19th October 2007, 04:48 PM   #3
chrisbp is offline chrisbp  United Kingdom
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I have just found this pair on ebay which are the same as my pair - http://i7.ebayimg.com/05/i/000/b7/f2/4586_10.JPG

The basic amp is available in three models - these can be seen on this site: http://www.hi-end.on9mart.com/index.html

The mono amps are available as EL34, KT88 and 300B The EL34 and KT88 versions have the same tubes (6N1, 5Z4P and the magic eye / 6E2), but the 300B version has a completely different set of tubes - and I notice it weighs more - so I guess it is different internally)

Does anyone know if it is possible that its just a case of swapping over to a KT88 in my case?

Cheers
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Old 19th October 2007, 07:40 PM   #4
hnb2907 is offline hnb2907  United Kingdom
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Quote:
Originally posted by chrisbp
I have just found this pair on ebay which are the same as my pair - http://i7.ebayimg.com/05/i/000/b7/f2/4586_10.JPG

The basic amp is available in three models - these can be seen on this site: http://www.hi-end.on9mart.com/index.html

Cheers

HI Chris,

I also looked at buying these from the same seller, before I bought the amp I have got.

I'm only a beginner to playing around with valve amps, but what I would suggest you do before anything else is to backwards engineer the schematics, and mark them up with all the voltages. Hey, I'm assuming that you're ok doing that... Watch out, don't get bitten!

My own amp was configured for 220VAC, and running it on 240VAC sent the heater voltages over the valve manufacturers high limit, and increased the B+ supply voltage. The first jobs were to add a 1M bleeder resistor to the B+ caps, then 10W series resistors to the heaters to bring them back to ~6.3V, and add an extra B+ Resistor/Capacitor network in the PSU. Doing the latter reduced the AC hum in the speakers to virtually nothing on 90dB speakers.

I'm currently experimenting with some 120ohm NTC inrush thermistors on the primary side of the mains transformer. This also helps to reduce the transformer output voltages slightly, by dropping about 5V off the mains supply.

My own amp had a 5Z3P, which can be directly replaced with a 5U4G. This gave me a bit more output voltage and ability to add a slightly bigger R/C filter to the B+ rail. Don't think it made any major difference to the sound, but it looks better
A quick trawl around t'interweb, I think you can use a GZ32 in place of the 5Z4P. Check the output voltage before and after changing it though.

My preference for EL34 is Svetlana, and with the help of some folks on the forum, I believe that they're the old St Petersburg style. I previously had ElectoHarmonix EL34EH in them, which were fine, but somehow the Svetlana's just do it for me.

Any chance you can take a few pics of the inside of one of your monoblocks? The main reason I didn't buy a pair of those, was because I couldn't see what the inside contained and what the build standard was like....


Cheers,
Chris.
ps: apologies, I forgot to find out how much electronics knowledge you have!?
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Old 19th October 2007, 07:55 PM   #5
chrisbp is offline chrisbp  United Kingdom
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Quote:
Originally posted by hnb2907



HI Chris,

I also looked at buying these from the same seller, before I bought the amp I have got.

I'm only a beginner to playing around with valve amps, but what I would suggest you do before anything else is to backwards engineer the schematics, and mark them up with all the voltages. Hey, I'm assuming that you're ok doing that... Watch out, don't get bitten!

My own amp was configured for 220VAC, and running it on 240VAC sent the heater voltages over the valve manufacturers high limit, and increased the B+ supply voltage. The first jobs were to add a 1M bleeder resistor to the B+ caps, then 10W series resistors to the heaters to bring them back to ~6.3V, and add an extra B+ Resistor/Capacitor network in the PSU. Doing the latter reduced the AC hum in the speakers to virtually nothing on 90dB speakers.

I'm currently experimenting with some 120ohm NTC inrush thermistors on the primary side of the mains transformer. This also helps to reduce the transformer output voltages slightly, by dropping about 5V off the mains supply.

My own amp had a 5Z3P, which can be directly replaced with a 5U4G. This gave me a bit more output voltage and ability to add a slightly bigger R/C filter to the B+ rail. Don't think it made any major difference to the sound, but it looks better
A quick trawl around t'interweb, I think you can use a GZ32 in place of the 5Z4P. Check the output voltage before and after changing it though.

My preference for EL34 is Svetlana, and with the help of some folks on the forum, I believe that they're the old St Petersburg style. I previously had ElectoHarmonix EL34EH in them, which were fine, but somehow the Svetlana's just do it for me.

Any chance you can take a few pics of the inside of one of your monoblocks? The main reason I didn't buy a pair of those, was because I couldn't see what the inside contained and what the build standard was like....


Cheers,
Chris.
ps: apologies, I forgot to find out how much electronics knowledge you have!?

Cheers, I have little knowledge - not enough to do what you suggest! Now the bleedin magic eye tube on one of them has gone all dull! (had them 2 days) - amp works okay still.

Cant say Im very impressed with them. Bass seems a bit boomy and does not go down as far as my old Inca Designs 75 unit - thats why I want to change to KT88s to see if that helps.

Im probably going to send them off to get them looked at / checked over - this place looks like they have worked on some Chinese kit before - http://www.chambonino.com/index.html

I will take some photos for you.

Cheers,

Chris
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Old 19th October 2007, 08:06 PM   #6
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Stock chinese output transformers usually means that it doesn't much matter what valves you stick in there...

Really good output transformers are hard to build and can't be done cheap and quick.

But who knows, chinese people are exceptionally clever and the OPT's might just be well built using a tried and true japanese design and special trade secrets that have never been shared with anyone else before...

Sarcasim aside, if they are new then first see how they sound after a month or so of solid playing.

I do sincerly hope they don't fizzle out due to electrical problems with the power supply
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Old 20th October 2007, 09:28 AM   #7
chrisbp is offline chrisbp  United Kingdom
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[QUOTE]Originally posted by soulmerchant
[B]Stock chinese output transformers usually means that it doesn't much matter what valves you stick in there...

Really good output transformers are hard to build and can't be done cheap and quick.

But who knows, chinese people are exceptionally clever and the OPT's might just be well built using a tried and true japanese design and special trade secrets that have never been shared with anyone else before...

Sarcasim aside, if they are new then first see how they sound after a month or so of solid playing.

I do sincerly hope they don't fizzle out due to electri
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Old 20th October 2007, 09:34 AM   #8
chrisbp is offline chrisbp  United Kingdom
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Dont know if this helps - a pic of the transformers. The largest is 9.75 cm wide. It seems very well made inside - all point to point wiring.

Any opinions on these transformers? Is it worth investing any money upgrading tubes etc - or are the transformers the limiting factor?

Cheers
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Old 20th October 2007, 09:55 AM   #9
Cobra2 is offline Cobra2  Norway
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They look better than many other I have seen...

Arne K
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Old 20th October 2007, 12:30 PM   #10
hnb2907 is offline hnb2907  United Kingdom
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Quote:
Originally posted by chrisbp
Dont know if this helps - a pic of the transformers. The largest is 9.75 cm wide. It seems very well made inside - all point to point wiring.

Any opinions on these transformers? Is it worth investing any money upgrading tubes etc - or are the transformers the limiting factor?

Cheers
Hi Chris,

It looks quite tidy from the pic, thanks!

Personally, I'd go for replacing capacitors in the audio paths and the valves first.

It's a cheaper option than swapping transformers. From my experience of upgrading 2 speaker amps and 1 headphone amp (all valves), it has made a significant improvement to the clarity of sound and bass response.... You can always do the transformers later, if you want to.

Check my "hnb2907" post on here for a discussion of the upgrades I've done to my headphone amp. It's not exactly akin to this discussion, but gives you a clue to some of the improvements made.


Cheers,
Chris.
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