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Old 2nd June 2011, 05:37 AM   #1
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Unhappy I think I made a mistake

I got those amp: Mono 6B4G tube amp and Preamp - Canuck Audio Mart
from someone who built those tube amp. I was so excited that I didnt really cared about a couple issue, and litteraly, the sound. I'm used to SS amp, so at first listening, I was super impressed, but now, 600$ later, and a couple of listening test, I'm a little less happy.

First of all, there's not a hum like written in the ad. However, they are super sensitive. If I walk to hard on the floor, it may have the little "shhhh" nsound. Hard to eplain but I'm sure what I mean. Sort of a electro-static sound?


Second of all, the sound. While not bad, there's something just not right. IT lacks dynamic, soundstage, presence? Hard to explain. The bass is nice. The midrange is aggressive, strong. Sound good at first sight, but tends to be irritating after a while!!! I paid 600$ for this, and damn, I dont know what to do.

Can anyone be gentle enough to take a look at the pictures, and tells me things to change in order to give this amp a second life? What can be wrong, what shouldn't be there.

ps: I wil have the schematic soon. the technician is out of town for a while...

It's in push-pull configuration...

I know that a crazy request, but I really don'T know where to start neither what to do. I can use this forced "project" to get my hand dirty for the fist time and learn some stuff about tube amp. My hope is that this amp's got potential that just need to be unleashed?.........

thanks
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Old 2nd June 2011, 05:52 AM   #2
tomchr is offline tomchr  United States
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Damn. That's a bummer. But it may be fixable. I bet once you get a schematic drawn up, you'll get some helpful responses.

Tubes are somewhat sensitive to vibration. That may be what you hear when you stomp on the floor or tap the tubes (carefully!) with the eraser end of a pencil. That's pretty normal. Some tubes are optimized for low microphonics. I don't know if 6B4G is one of them. I'm guessing not... You could place the amp on some sort of suspension. Think the kinds of stuff people use for their turntables.

~Tom
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Old 2nd June 2011, 06:14 AM   #3
Namatko is offline Namatko  United States
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Tubes in an amp shouldn't be so sensitive that walking on a relatively solid floor near them causes noise. Probably one of them has developed a loose mount inside the tube and become badly microphonic. I have replaced many tubes in music amps for that problem. It can also cause distortion by the electric field inside the tube causing the loose mount to vibrate.
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Old 2nd June 2011, 08:38 AM   #4
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The wiring and construction looks a little "dodgy". Seems that it was put together in a hurry and worse, banged around a lot, especially the preamp. The transformer on the power amp also looks damaged. I think a few forumers did warn you against these points earlier regarding this amp.

Anyway, maybe you will have to go through the connections and solder points one by one and make sure there are no loose connections/dry joints ( a major cause of unidentified noise especially when it is so sensitive to vibrations ). The banging around probably contributes the most to this problem.

Get the schematic and let us have a look so that we can get some pointers as to your problems.

Last edited by quikie22; 2nd June 2011 at 08:59 AM.
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Old 2nd June 2011, 09:03 AM   #5
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Quote:
Originally Posted by jasonthegreat View Post
Second of all, the sound. While not bad, there's something just not right. IT lacks dynamic, soundstage, presence? Hard to explain. The bass is nice. The midrange is aggressive, strong. Sound good at first sight, but tends to be irritating after a while!!! I paid 600$ for this, and damn, I dont know what to do.
That sounds like not quite enough gNFB to clean up the H3 and take the edge off. Need to see a schemo, though.
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Old 2nd June 2011, 11:05 AM   #6
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Quote:
Originally Posted by jasonthegreat View Post
I got those amp: Mono 6B4G tube amp and Preamp - Canuck Audio Mart

First of all, there's not a hum like written in the ad. However, they are super sensitive. If I walk to hard on the floor, it may have the little "shhhh" nsound. Hard to eplain but I'm sure what I mean. Sort of a electro-static sound?

Could be an unused grid pin just floating and picking up anything (which it will). The lower part of the amp chassis is wood correct ? No screening !
If I take the lower cover off my tube preamp and put the unit on top of the CD player.....it picks up the mpu clock noise.

richy
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Old 2nd June 2011, 11:15 AM   #7
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I found with my DHT amp that the sound improved surprisingly when I changed from AC heating to a Coleman type system. It appears that in DHT's the heating arrangements matter much more in say dynamics than regards to hum than you would expect.

There's solid advice by previous posters, my advice would be to try out at least CCS heaters on the DHT's.
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Old 2nd June 2011, 04:08 PM   #8
Jeb-D. is offline Jeb-D.  United States
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The noise you describe sounds like microphony, which seems to be fairly common for direct heated triodes.

Even if the sound isn't quite where you want it, I think you made out pretty good on the deal. I usually end up spending $600+ in parts and shipping alone to build something comparable. It may just require a little tweaking. Even if it needs a re-design you have tubes, iron and chassis.

The other thing is that lower powered tube amps with little to no feedback are very picky in the speakers you try to pair them up with. Not nearly as flexible or forgiving as solid state amps or high feedback high powered tube amps. But when you do find the right match, it's capable of sounding very good.
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Old 2nd June 2011, 04:40 PM   #9
kevinkr is offline kevinkr  United States
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Construction quality leaves a lot to be desired, but there are a lot of good parts inside and you have the making for a good amplifier I believe.

I'm not a fan of the particular coupling caps used - I've found them to be quite colored sounding. (This of course is a subjective opinion) I'd recommend the inexpensive Russian Teflon FT-3 type as a possible replacement - it's sonically and electrically better. (No issue with leakage currents as they age either.)

Not necessarily the case that this design uses global feedback, my PP triode amps don't, but without seeing the schematic it is hard to know.

IMLE the 6B4G is quite microphonic as are many dht power tubes, the solution is to make sure they are well isolated from footfalls and other sources of vibration. They can also vibrate in tune to the music with some interesting and unwanted results - I have had actual cases of acoustic feedback with the 26 dht in low level stages - the problem with power tubes is not usually this severe.

The speakers you are using may or may not be synergistic with this amp as designed - what are they exactly?

I think you have the platform for a very good set of amplifiers.

The pre-amp is based on op-amps and could be a questionable choice IMHO for someone interested in an all tube system. If you have a CD player with variable out I would run that directly into the power amps and see what you end up with sonically just as a test. Choice of op-amps used can influence the performance in audible ways - in that vein what op-amps are used in this pre-amp?
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Last edited by kevinkr; 2nd June 2011 at 04:45 PM.
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Old 2nd June 2011, 06:49 PM   #10
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okay, well THATS encouraging!!!!!! I didnt get the pre-amp, only the tube amp.

The sensitivity is for both mono blocks. If I touch either one, the "problem" is there.

I dont have a schematic, now, so for now, I'll put this at hold.

I really hope I can get one, but bit scared that I wont, if I cant have a schematic, is it dramatic.

The thing is, the technician had a inondation (flood?) so for the moment, is really unavailable...

Thanks guys, this gives me hope! Really

BTW, I use some good old dynaco A-25's

Last edited by murphythecat8; 2nd June 2011 at 06:57 PM.
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