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BAT VK75SE, Bring back its reputation

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Posted on March 20, 2015 at 19:21:02
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 I recall I post a review in here last year end, saying my used VK75SE Sounded grainy and thin, well it was all because of the leaky oil coupling caps!

Replacing them with Auricap XO, the midband harmonic richness and smoothness reappear but the dynamic seemed decreased

Finally replacing them with 0.33uF 600V Relcap RT, the VK75SE now give you the best of everything, midband richness and smoothness, full range very dynamic, solid clean strong bass, huge sound stage and dimensionality, dellicate airy high, the sound is so full ,lush, and clear and 3D, just can't say enough about it. To compare with the ARC VSI60 I just
sold, the BAT beat the ARC handsdown

I wish Victor is here to read this post and I sincerely apologize for my previous post. The VK75SE is really the classic tube amp which set the new standard for how a good amp should sound.




 

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RE: BAT VK75SE, Bring back its reputation, posted on March 20, 2015 at 20:20:47
Cougar
Audiophile

Posts: 4583
Location: SoCal
Joined: June 25, 2001
 the BAT uses Jensen Copper foil caps that go bad in time. I have a BAT VK-30 that the same thing happened. I replaced with new Jensen Copper Foil caps and the magic was back.

I wanted to put some Duelund Alexander caps in the BAT but that just too big to fit without major work. I will try my version of the 6 pak in my preamp.

BAT makes some of the best gear I have ever heard and soon I will have a BAT amp to go with my BAT VK-30. I'm still looking for a BAT P10 phono preamp.

 

RE: BAT VK75SE, Bring back its reputation, posted on March 20, 2015 at 23:17:25
Daverz
Audiophile

Posts: 2104
Location: So. California
Joined: September 24, 2002
 This amp can't be that old, can it? And the caps in this multi kilobuck amp are already leaky and require replacement?

 

RE: BAT VK75SE, Bring back its reputation, posted on March 20, 2015 at 23:45:00
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 When I took out those oil caps from the VK75SE. One pc had obvious leakage that the oil coming out from the edge of the cap.

I once tried the Jensen copper oil cap in another DIY project. The Jensen cap at the time also sounded a bit thin in midrange and also not so full body in the midbass, I would advise Victor of BAT to try out RELCAP RT to re-evaluate his remarkable BAT tube amp

 

RE: BAT VK75SE, Bring back its reputation, posted on March 21, 2015 at 05:11:41
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Thanks! for sharing -EC.

 

Problem with amps using the 6c33c tubes, posted on March 21, 2015 at 13:09:16
morricab
Distributor or Rep

Posts: 9178
Location: switzerland
Joined: April 1, 2005
 THey get DARN hot! THat means capacitor lives for electrolytic and for PIO caps are severely shortened. I had OTLs using 4 of these tubes per mono and they had cap issues as well.

 

BAT's tend to have cap problems, posted on March 21, 2015 at 19:50:06
Justlisten2
Audiophile

Posts: 1266
Location: SE PA
Joined: March 8, 2001
 I've owned 9 pieces of BAT gear in my time, including a VK-75SE with cap issues, which I had modified by Bob Backert. He replaced them with V-Caps, wiring, and circuit mods, major improvement.
BAT gear sounds very dynamic and powerful, but a few had cap problems and had to be replaced. Those standard BAT caps are not very good, IMHO.
I don't buy BAT anymore.

 

RE: BAT's tend to have cap problems, posted on March 21, 2015 at 20:18:27
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 Electrolytic caps have temperature ratings.
Most standard caps are rated at 85 C. There are newer ones rated at 105 C and some even higher.

HEAT is the enemy here. The 6C33 tubes run damn hot, drawing huge filament current (8 amps, IIRC) I was asked to bring the amps in but one step into their demo room ended any possibility.

Cap life drops by a factor of 2 if the rated temperatures are reached. And the life is couple of thousand hours.

To be honest BAT is not the only manufacturer to ignore temperature ratings. The old Rappaport amps ran hot, hot, hot. Sounded good but never made it through a year ( early 80's). Mark Levinson ML-2's likewise: generated 400 watts of heat simply idling. Heat killed them. Working at a ML dealer in the early 80's not a single ML-2 made it through the warranty period.



 

RE: BAT's tend to have cap problems, posted on March 22, 2015 at 09:37:06
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 Well, one needs to be careful when making general statements.

Some of those amps in their initial configuration, VK-60's, are now close to 20 years old. But they are still running and running, we hardly see them back for service.

The way the amps are designed, the internal components only see very small temperature raises. The tubes are indeed running hot, the components are not. There is no issue with the electrolytic capacitor life in them, we replace few pieces now and then, due to normal random failures.

On subject of oil capacitor, there is a lot of confusion here. Some of the older style capacitors will leak a small amount of oil after a while - which is in those amps totally harmless. Several years ago the seal on them was improved, and we have not seen leakage in those. This should not be confused with the electrical leakage in the preamp output capacitors, where this will affect the operation. There is no such sensitivity in the power amps, up to the point of a complete capacitor failure, which happens VERY infrequently. Thanks to the self-adjusting nature of the bias circuit, a significant degree of parameter shifts can be easily accommodated.

BTW, those capacitors are aluminum, not copper.


 

RE: BAT's tend to have cap problems, posted on March 22, 2015 at 12:11:03
Justlisten2
Audiophile

Posts: 1266
Location: SE PA
Joined: March 8, 2001
 It's not only the amps though. I've had caps go bad in a VK-31SE, VK-50SE and VK-51SE preamp, as well as a VK-P10SE w/Super-Pak. Seems like a pattern when 5 out of the 9 pieces I've owned have had cap problems.
Like I said, they do sound good, but I have found other gear that sounds good too, that has a better track record as far as reliability goes.

 

RE: BAT's tend to have cap problems, posted on March 22, 2015 at 13:31:16
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 Victor, In VK75SE, is the 1st stage and 2nd stage direct coupled. I measured the voltage across the coupling cap (Output of 2nd driving stage to grid of 6c33c)is as high as 680V DC. Right now those RELCAP RTs I put in are 600V DC rating, Are they OK?

Regards,
Eric

 

RE: BAT's tend to have cap problems, posted on March 22, 2015 at 13:38:09
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 Yes, the first two gain stages are direct coupled. You need to be careful with the voltage rating of those caps. During the initial sequence, and depending upon the tube set, the voltage can exceed 700V, and some capacitors might not like that. The paper capacitors used in the 75SE can take up to 900V with no problem, according to the manufacturer, but typically the plastic parts don't have that kind of margins.


 

What about the VK42SE preamp?, posted on March 24, 2015 at 06:04:52
hinduclient
Audiophile

Posts: 984
Joined: August 14, 2002
 My VK42SE is just about 10 years old. What's the chances of having capacitor failure or other issues? What's the cost to have BAT replace old innards?

The 42se runs warmish but nothing like the tubed 50se that ran HOT.

 

RE: What about the VK42SE preamp?, posted on March 24, 2015 at 06:34:25
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 I am not sure if the leakage has anything to do with voltage applied on two ends of the oil coupling, the cap used in VK75SE is 690V which is very high indeed
The voltage across the cap in BAT preamp is much much lower, also, as described by Victor , the later production for the oil cap have better construction that prevent leakage

 

RE: BAT's tend to have cap problems, posted on March 24, 2015 at 08:16:01
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Thanks! for sharing. It would appear that BAT could build a better cap or have a better cap maker install their ware(s) into B.A.T. products?

 

RE: What about the VK42SE preamp?, posted on March 25, 2015 at 07:50:58
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 The voltage is not an issue, as all the parts operate well within their ratings, with room to spare. The issue is sometimes application specific. In preamps the capacitor electrical leakage will produce an audible effect - a pop. There is no such thing in the power amps.

Out of curiosity, I looked at the repair records for VK-60 - the first model using this basic topology, with some units 20 years old by now.

I looked at the factory repair records for the past 10 years. During that time we serviced about 60 units. And among them I counted 7 (seven) cases of various capacitor issues. 4 were bad Jensen capacitors, the others were various other parts.

Now, let's do a simple math. By a quick count, there are about 50,000 different capacitors in the VK-60 amps in use today. Of that number, over the period of 10 years, 7 needed replacement. Certainly, the factory repair records do not capture every case, but that should still give you some idea about the extent of the problem.

It kinda looks to me that the "idea" of hot running inferior parts inside those chassis is sort of out of luck. Not much proof of low quality parts there.


 

I looked at the data, posted on March 25, 2015 at 08:06:58
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 The 42SE has been in production since 2006. Since then, about 10 units came back to the factory for various reasons, including the damages. None required a capacitor replacement.

I don't remember exactly when Jensen redesigned the seal, but by memory it was about 10 years ago.


 

RE: BAT's tend to have cap problems, posted on March 25, 2015 at 18:00:03
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 I don't think there is ANY evidence, supporting this allegation.


 

RE: BAT's tend to have cap problems, posted on March 26, 2015 at 06:08:42
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Hopefully, the newer offerings from BAT have a better design and/or uses better caps & parts. When I think about the prices for the REX editions, (1) unit that does not perform, is too much.

 

RE: BAT's tend to have cap problems, posted on March 26, 2015 at 06:42:23
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 Above I provided the data on old design, that clearly shows no issues at all with its parts or their application. 7 failed parts out of 50,000 over the period of ten years is the record anyone would be proud of.

The only area where there was some issue was one part in one application, specifically - the preamp output capacitor, but that part was improved by Jensen as soon as the problem was discovered about ten years ago. But even that had low frequency of occurrence. Specifically, 2.5% of them failed in TEN years. To us it was still significant enough to worry about. To the best of my knowledge there have been no such failures since the redesign.

Speaking objectively, there is simply no evidence at all to support the notion that "BAT's tend to have cap problems".


 

RE: BAT's tend to have cap problems, posted on March 26, 2015 at 08:16:53
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Excellent data -Victor. I see you are listed as a "manufacturer" - what do you make/produce?

 

I am one of the BAT guys. nt, posted on March 26, 2015 at 08:31:06
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 .


 

RE: I am one of the BAT guys. nt, posted on March 26, 2015 at 10:55:10
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Outstanding- Victor.
are there are new product(s) being released this year?

 

RE: I am one of the BAT guys. nt, posted on March 26, 2015 at 14:01:13
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 Yes, of course... they will appear very soon on our web site. Two solid state preamps, one new solid state amp, and I hope to have more this year.


 

RE: I am one of the BAT guys. nt, posted on March 26, 2015 at 16:07:34
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 Regarding your website, it would be helpful to list all U.S.A dealer/retailers.

 

RE: I am one of the BAT guys. nt, posted on March 26, 2015 at 17:13:15
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 I think our sales force feels our network is not yet finalized, I know they have been making some changes.


 

RE: I am one of the BAT guys. nt, posted on March 27, 2015 at 05:30:50
fantja
Audiophile

Posts: 15519
Location: Alabama
Joined: September 11, 2010
 This aspect of your website would be most-helpful.

 

RE: I am one of the BAT guys. nt, posted on March 27, 2015 at 05:45:30
Victor Khomenko
Manufacturer

Posts: 55318
Joined: April 5, 2000
 I will mention that to our people responsible for it, I am just a technical guy! :) I hear people argue it both ways.


 

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