One used to be able to pick up tube testers at military auctions. Not sure if is true anymore. Got my Hickok for $75
What Audio Research power amps have you owned or admired?
- Thread starter Jay_S
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One used to be able to pick up tube testers at military auctions. Not sure if is true anymore. Got my Hickok for $75
Back in 1998 I had for a short time 2 VT100 driving my Audio Artistry Dvorak dipole speakers (one for main panel and one for the dipol bass). Very special and good sound but the heat from 2 VT100 was simply to much even for me living in cold Sweden!
The agent for Audio Artistry was setting up the system while me and mý wife was away for the evening. We get back much earlier that we have said finding the agent i his underpants due to the heat in the room. He found it very embarrasing but since we afterwards become close friends we have had many laughs of the incident- And the sound was truly fantastic!!
The agent for Audio Artistry was setting up the system while me and mý wife was away for the evening. We get back much earlier that we have said finding the agent i his underpants due to the heat in the room. He found it very embarrasing but since we afterwards become close friends we have had many laughs of the incident- And the sound was truly fantastic!!
Yes, the VT 100 can put out some heat. But the Mark IIs and higher have fans and you can easily add on to the Mark I.
Several of my friends has VT100 mk 1 and mk II back in late 90ies. They where convinced that the Mark 1 was better than the MKLII. I don t know about MkIII
I had a VT-100 MKII and sold it because of the way crazy bias procedure. The amp top plate has a zillion screws and the side plates have a couple zillion more. You have to remove the top and both sides to bias this amp. And this isn't a simple bias procedure after you disassemble the amp either. That's why Kevin Deal from Upscale Audio refuses to sell tubes sets for any of the VT-100 series amps.
On the subject on fans on tube amps, I understand built in fans for some amps act as suction or exhaust rather than directly blowing to cool the tubes and amp. I read long time ago that directly blowing air from a fan into tubes can cause cracks or micro cracks to the tubes. Is this really correct? I've seen a few people here using an electric fan to directly blow towards the amp to dissipate the heat around it but so far have not heard anyone having tube failure with this practice.
Yes, I believe the fans pull the heat away but I have a Mark I with no fan so I am not 100%.
HI jadis,
Maybe the idea that a direct air flow on the tubes is bad has merit but my D250 does not seem to suffer problems. The four fans are horizontally mounted at the very bottom of the chassis and blows air directly vertically. They constitute a nearly continuous fan surface almost the size of the bottom of the chassis. They are fairly large fans.
The tubes (all 32 of them) are mounted horizontally directly in the air flow. The fans are low volume types for low noise and don't move a huge amount of air. They are pretty quiet. If you place your hand over the covers vent holes you will feel air flow but its not a blast. The fans are pretty effective because the cover never gets hot enough to burn your hand. It's warm but not hot.
I would say that this scheme is not based on a chimney effect.
There is only a single fan speed; well two, on and off. If the amp is turned on the fans operate continuously, even in standby.
Sparky
Maybe the idea that a direct air flow on the tubes is bad has merit but my D250 does not seem to suffer problems. The four fans are horizontally mounted at the very bottom of the chassis and blows air directly vertically. They constitute a nearly continuous fan surface almost the size of the bottom of the chassis. They are fairly large fans.
The tubes (all 32 of them) are mounted horizontally directly in the air flow. The fans are low volume types for low noise and don't move a huge amount of air. They are pretty quiet. If you place your hand over the covers vent holes you will feel air flow but its not a blast. The fans are pretty effective because the cover never gets hot enough to burn your hand. It's warm but not hot.
I would say that this scheme is not based on a chimney effect.
There is only a single fan speed; well two, on and off. If the amp is turned on the fans operate continuously, even in standby.
Sparky
Well, heat rises. The fans are mounted in the bottom of the amp and the heat vents through the top. I would call that a chimney effect. It really doesn't matter anyway. The fans are there to help draw the heat out of the inside of the amp and allow it to run cooler. How's that for an explanation?
Hi Sparky,
In your D250, that answers my question as now I hear a case where the fans, though not high powered, are blowing directly upwards against the tubes, as opposed to blowing downwards which will have an exhaust fan effect throwing the heat downwards. Thanks for sharing.
http://www.maximatcher.com/maximatcher.html
The maximatcher is a modern output tube tester.
I have an ARC D70 Mk II, I biased it myself, based on the owner's manual. This is the first time I've biased a tube amp. I've never done it before. The trick is to get to the test points easily. With the amp off, I used minigrabbers to access the TP pairs.
The maximatcher is a modern output tube tester.
I have an ARC D70 Mk II, I biased it myself, based on the owner's manual. This is the first time I've biased a tube amp. I've never done it before. The trick is to get to the test points easily. With the amp off, I used minigrabbers to access the TP pairs.
No idea, I just found that site and references to it when I was searching on-line for output tube testers.
Measurement Functions Plate Current (Ip) Range: 0 to 120.0 mA DC, ± 1.5 %
Transconductance (Gm) Range: 0 to 19.99 millimhos,
± 1.5 %
I don't think there's anything current that is more accurate other than the Amplitrex. Old testers always need to be calibrated and don't work at real world voltages.
Thing is, most tubes need a 48 hr burn in before testing and optimally, should be tested in the circuit being used. But if you're using NOS tubes, that's not an option; in addition, if you use something like a cj amp (unlike say VTL), there's no way of telling which output tube failed when the protective fuse blows (unless you're lucky enough to see which tube goes cherry red).
As far as I know, you're well advised to replace the caps in these many of these old amps you folks are mentioning. If there is any hum In the amp whatsoever, even if you almost didn't know it was there at all, replacing the filter caps (mains caps, power caps, the BIG electrolytics) on your amplifiers can cause it to magically disappear. To all vintage ARC and VTL owners I urge you to do this. Digikey. Come on in, the water's fine! You'll be amazed at how quiet your amps will be.
Now that the amplifier is properly biased measure and register the voltage between the 4 ohm and 0 ohm and between the 4 ohm and 16 ohm terminals without the speaker cables. You can use these points to check or re-bias next time without the minigrabers.
Most testers measure the tubes too far from the ARC operation points - Vanode = 420 V and Icathode = 65 mA
Bought a new d120 solid state when it first came out. And with it a new sp-8 pre-amp. A d76a amp. Started my son's high end journey===got him a d76/ls 1 preamp/and he uses that d120 in his bi-amped audio research setup. He uses cd's and I am all vinyl.
I have used their products-- collectively, added up-- for 80 years. In that time--aside from tube replacement--a total of 5 repairs. And the re-tubing costs exceeded the repair costs.
So I am all in on the older Audio Research equipment anyway.
I have used their products-- collectively, added up-- for 80 years. In that time--aside from tube replacement--a total of 5 repairs. And the re-tubing costs exceeded the repair costs.
So I am all in on the older Audio Research equipment anyway.
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I just found out something re the biasing of modern ARC amps. For example, they ask you to set the bias of the V1 tube at 65mA, and check its partner V3 tube so that it is in the 57-73mA range. My latest re tubing caused one set to be at 65mA for the first tube and 76mA for its partner tube. I felt uncomfortable with the 76 reading so I wrote ARC and the they said I can actually lower the 65mA so that its partner tube goes down to the 73 or below level. That the 65mA can stray within a +/-7mA level. That I never knew before.
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