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Old 4th October 2006, 10:07 PM   #1
Matt is offline Matt  United Kingdom
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I'm looking for a manual for ARC VT50 or a copy or scan as I have bought the amp but no manual. Need it to check how to rebias new valves. Can any one help or tell me what to do?

Thanks all

Matt
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Old 5th October 2006, 04:33 AM   #2
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Matt,

Try searching around here: http://www.arcdb.ws/

Also try contacting them for a manual or instructions.

http://www.audioresearch.com/

Victor
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Old 5th October 2006, 03:41 PM   #3
Matt is offline Matt  United Kingdom
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Thanks Victor

I've looked about everywhere including the AR Db site. Apparently ARC don't sell manuals and in anycase it would mean ringing them as there is no contact email address and that isn't easy due to the time difference.

All I'm really trying to get is some details on how to re-bias new valves.

Thaks for reading though. Any other ideas?
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Old 5th October 2006, 03:45 PM   #4
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Quote:
Apparently ARC don't sell manuals and in anycase it would mean ringing them as there is no contact email address and that isn't easy due to the time difference.
Send a letter?

If you can find a time to call them, I would do that. For many years I owned ARC products, and I was always pleased with ARC's friendly and helpful service staff (no affiliation).
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Old 5th October 2006, 04:26 PM   #5
Matt is offline Matt  United Kingdom
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Thanks Brian.

Good shout! So used to emailing tend to forget about the 'old' ways!!!

I'll write with my details etc. Hope you are right about their service their agent in UK doesn't have a particularly good cutomer service record!

Matt
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Old 5th October 2006, 05:32 PM   #6
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Actually AR does sell manuals. At least they used to because I've bought some in the past to get the schematic. At some point they began leaving out compont values from the diagrams to foil us builders I suppose. And for them not to have an email addy stinks. They want to push their products for big money but can't be bothered to communicate.

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Old 5th October 2006, 06:52 PM   #7
Matt is offline Matt  United Kingdom
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Clearly they don't feel they have to! Strange for a big company particularly and American one. Have to admit that in relation to customer service US companies tend to be the best. Strange this one doesn't even have an email!!! I will give them a try. Thanks for idea. I was hoping some one out there might have a manual which would save me the time.
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Old 6th October 2006, 03:00 AM   #8
James A is offline James A  United States
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Model VT50

"Output Tube Bias adjustment
As shipped from the factory, the output "bias" adjustments are set for a nominal 65mA per 6550 tube. Under these idle conditions the tubes are dissipating aproximately 27 watts of their 41 watt rating (35 watt plate, 6 watts screen). This point of operation provides "enriched" Class AB 1, and will satisfy the most critical listener."

"For best results, operate and adjust the VT50 at the normal rated line voltage listed on the rear panel. Adjustment must be made under zero-signal conditions after at least 15 minutes of uninterrupted stabilization time."

"A digital voltmeter capable of accurate measurements with 1mVDC resolution is preferred for accurate adjustment (must have 3 1/2 digit display). Use the plastic alignment tool provided to make the adjustment. the test points are accesible from the top of the circuit boards above the output tubes. Adjust the "bias on each channel for an average reading of 65mVDC (0.065 volt DC) Caution: resistor is 420V above ground."

=====================================

Just a couple of notes from me:

If the new tubes you bought are not pre burned- in you will be readjusting the bias several times for about the first 50 hours of use. As you will discover it can be a real pain in the butt.

Before you start, do you have the plastic screw driver to set the pots? if not buy one. I would not use a metallic screw driver.

Also before you start,..... with the old tubes still installed in the Amp check the bias voltage as decribed in the above ARC instructions. Lower the bias voltage down to around 58 to 60mVDC. This is also a good opportunity to practice and get the feel of the pot/s movements and adjustments. You will appreciate it greatly when you finally set the bias voltage for the new tubes.

Turn off the Amp and let it cool down. Now change out the tubes. Turn on the amp and after just a few minutes check the bias voltage. At this point just make sure it is not too high. If the bias voltage is too high you could damage your new 6550 power tubes. That is the reason I gave for backing off the bias voltage before you pulled the old tubes. If it is above 70mDC, (0.070VDC) back the pots down slightly to around 62 to 65mVDC. After about 15 minutes check the bias voltage again. If the 6550 power tubes were not pre burned-in I would not put the top cover back on yet. play some music for a few hours and follow ARC bias adjustment procedure again.


Hope this helps....
Jim
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Old 6th October 2006, 06:53 PM   #9
Matt is offline Matt  United Kingdom
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Jim That is fantastic thank you. Only one little thing though where do you place the probes to test the voltage? I have details on the VT100 but not the 50. As I understand it there is a 'biasing resistor' placed near the top of the boards on each side but don't want to get it wrong!!! This is the first tube amp I've owned. Listened to other peoples and wanted one for a long time. Also is there any different adjustments to make when replacing the driver tubes?

Thanks again, greatly appreciate your help.
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Old 6th October 2006, 08:30 PM   #10
James A is offline James A  United States
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Matt,
There is a resistor near the top of the circuit board for each CH. The resistors are centered above the top two 6550 tubes of each CH. Just above the resistors you will see silver colored print that says "Test Points" If you look at the left side of the Amp, the Left CH, you will see a square blue adjustment pot just to the left of the top front 6550 tube. Above the pot is the words "bias adjust". For thr Right CH, right side of amp, to the right side of the top front 6550 tube you will find the bias pot for the Right CH. These two pots are the only adjustments needed. Be very careful when you do your adjusting, those 6550 tubes get mighty hot....


Did you buy pre burned-in 6550 tubes?

What is the rest of the make up of your system?

jim
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