Matt,
Try searching around here: http://www.arcdb.ws/
Also try contacting them for a manual or instructions.
http://www.audioresearch.com/
Victor
Try searching around here: http://www.arcdb.ws/
Also try contacting them for a manual or instructions.
http://www.audioresearch.com/
Victor
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?
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?
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.
Victor
Victor
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.
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
"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
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.
Thanks again, greatly appreciate your help.
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
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
HI Jim
Thanks very much. No I've not bought new tubes but I've bought the amp second hand and anticipate the need to change them. Your advice has been perfect. I haven't opened the lid and didn't want to untill I had the info because the temptation to tamper is too great. I have an analogue meter which I don't think I will use I will purchase a digital one as everything suggest that.
As for my system. ARC CD3 Mk3, ARC LS15 and now the VT50. The amp replaces Michell Alecto monoblocs. Speakers are Cloned Proac 2.5s using this forums advice.
I started with the CD3 as my old Denon although good was clearly not doing justice. Once I had that and havng heared ARC system with Proacs some years ago I knew I wanted to go that way. Always been put off tubes because of the 'problems' of biasing and replacing but in the end it is about sound isn't it and tubes are my sort of sound. The Alectos were great and give a tube sort of sound but just arent as transparent as tubes.
Thanks again to every one. Most helpful - more than that actualy without the advice I'd be stuck, without the manual!
Thanks very much. No I've not bought new tubes but I've bought the amp second hand and anticipate the need to change them. Your advice has been perfect. I haven't opened the lid and didn't want to untill I had the info because the temptation to tamper is too great. I have an analogue meter which I don't think I will use I will purchase a digital one as everything suggest that.
As for my system. ARC CD3 Mk3, ARC LS15 and now the VT50. The amp replaces Michell Alecto monoblocs. Speakers are Cloned Proac 2.5s using this forums advice.
I started with the CD3 as my old Denon although good was clearly not doing justice. Once I had that and havng heared ARC system with Proacs some years ago I knew I wanted to go that way. Always been put off tubes because of the 'problems' of biasing and replacing but in the end it is about sound isn't it and tubes are my sort of sound. The Alectos were great and give a tube sort of sound but just arent as transparent as tubes.
Thanks again to every one. Most helpful - more than that actualy without the advice I'd be stuck, without the manual!
Hi Jef
Thanks for that I've just purchased a manual from the UK distributor they charged about 30$ and didn't includ a screwdriver!!!
If I could contact ARC in USA I would but you have to phone or write both of which are quite an inconvinience. Mind you what the UK distributor charge might make it worth it!
Do you like your VT50?
Thanks for that I've just purchased a manual from the UK distributor they charged about 30$ and didn't includ a screwdriver!!!
If I could contact ARC in USA I would but you have to phone or write both of which are quite an inconvinience. Mind you what the UK distributor charge might make it worth it!
Do you like your VT50?
Matt,
Just picked it up the other day but so far I am very pleased. Big and powerful soudstage, refined and detailed midrange with very nice treble extension and air. I am using it as a mains amp in a home theatre setup with a lexicon MC1 so it leans a bit to the dry side for me. I may try a set of KT90s to fatten up the sound. Using the LS 15 I imagine you don't have that issue. Now I just need to find another one for the surrounds.
Jeff
Just picked it up the other day but so far I am very pleased. Big and powerful soudstage, refined and detailed midrange with very nice treble extension and air. I am using it as a mains amp in a home theatre setup with a lexicon MC1 so it leans a bit to the dry side for me. I may try a set of KT90s to fatten up the sound. Using the LS 15 I imagine you don't have that issue. Now I just need to find another one for the surrounds.
Jeff
>>"I am using it as a mains amp in a home theatre setup with a lexicon MC1 so it leans a bit to the dry side for me. I may try a set of KT90s to fatten up the sound.
>>>>>>>>>>>>>>>>>>>>>>>>>
The VT50 is in no way a lean sounding amp. More than likely it is the preamp, or maybe the ics, speaker cables, or the speakers connected to the amp.
What brand of tubes are you running in the amp? I have had good luck using EH tubes. I have my bias voltage set at 65mVDC.
Preamp, Sonic Frontiers Line one. (tubes) present time early 60s Siemens, dull grey plate, CCa.
ics Audioquest Diamond X2
Speakers, ProAc Studio 200
Speaker cables, Audioquest Sterling 3.
=============
Just a suggestion, if you want a warmer smoother more layed back sound, back off the mVDC a tad. Instead of running the voltage at 65 mVDC cut it back to around 60 to 62 mVDC. You will loose some of the detail though.
Before I bought the Sonic Frontiers preamp I was using an ARC LS3 SS preamp I was somewhat experiencing the sound from my system as you have decribed. Backing off the bias voltage did help.
If you give it a try post back with your results.
Jim
>>>>>>>>>>>>>>>>>>>>>>>>>
The VT50 is in no way a lean sounding amp. More than likely it is the preamp, or maybe the ics, speaker cables, or the speakers connected to the amp.
What brand of tubes are you running in the amp? I have had good luck using EH tubes. I have my bias voltage set at 65mVDC.
Preamp, Sonic Frontiers Line one. (tubes) present time early 60s Siemens, dull grey plate, CCa.
ics Audioquest Diamond X2
Speakers, ProAc Studio 200
Speaker cables, Audioquest Sterling 3.
=============
Just a suggestion, if you want a warmer smoother more layed back sound, back off the mVDC a tad. Instead of running the voltage at 65 mVDC cut it back to around 60 to 62 mVDC. You will loose some of the detail though.
Before I bought the Sonic Frontiers preamp I was using an ARC LS3 SS preamp I was somewhat experiencing the sound from my system as you have decribed. Backing off the bias voltage did help.
If you give it a try post back with your results.
Jim
Hello Jim,
Thanks, all good ideas, I am fairly certain the leaness resides in the Lexicon processor and I have heard that of the possible tube types kt90s offer the fattest sound.
As for speakers, all are DIY, built in my basement shop.
Mains are a dual woofer 2way with Morel MDT 33s and Scanspeak 8645s
Surrounds are small 2way with Morel MDT30s and Dynaudio 15w 75s
Subs (2) are NHT 1295 in a 4cu ft sealed box powered by a Parasound HCA 1000
I use a Musicap high pass in the linestage so the mains are free to sing.
Thanks,
Jeff
Thanks, all good ideas, I am fairly certain the leaness resides in the Lexicon processor and I have heard that of the possible tube types kt90s offer the fattest sound.
As for speakers, all are DIY, built in my basement shop.
Mains are a dual woofer 2way with Morel MDT 33s and Scanspeak 8645s
Surrounds are small 2way with Morel MDT30s and Dynaudio 15w 75s
Subs (2) are NHT 1295 in a 4cu ft sealed box powered by a Parasound HCA 1000
I use a Musicap high pass in the linestage so the mains are free to sing.
Thanks,
Jeff
Just one more thing if any one is reading this.
When you adjust the biasing is says under zero condions which means as i understand it no input signal so not to attach in put leads. What about output? Does there need to be a laod on the output? Attaching the speakers for instance do I need to do that or can all the adjustments be made on the bench?
Thanks for this.
Matt
When you adjust the biasing is says under zero condions which means as i understand it no input signal so not to attach in put leads. What about output? Does there need to be a laod on the output? Attaching the speakers for instance do I need to do that or can all the adjustments be made on the bench?
Thanks for this.
Matt
Did you know?
This is a very old thread.
How many of you with the ARC VT50 know the 6922 tubes need to be biased when replacing them?
It is true!
The first thing that is a must is to buy 6922 tubes with closely matched section 1 and section 2 triodes. That is a must. If the triodes of each tube are not closely matched you will not be able to set the plate voltages properly for the input and driver 6922 tubes of each channel. Especially the driver tubes.
VT50 re-tubing setup instructions
http://www.audioresearch.com/ContentsFiles/VT50_BiasAdjust.pdf
VT50 wiring Schematic
http://www.audioresearch.com/ContentsFiles/VT50_SchemPL.pdf
Three trim pots are found behind the side panels on the right and left side of the amp.
I recommend meter leads clip on hook probes be used for making the necessary adjustments. Be careful, lethal DC voltage inside. Not to mention the damage that could be done if a probe shorted across a power trace.
Jim
This is a very old thread.
How many of you with the ARC VT50 know the 6922 tubes need to be biased when replacing them?
It is true!
The first thing that is a must is to buy 6922 tubes with closely matched section 1 and section 2 triodes. That is a must. If the triodes of each tube are not closely matched you will not be able to set the plate voltages properly for the input and driver 6922 tubes of each channel. Especially the driver tubes.
VT50 re-tubing setup instructions
http://www.audioresearch.com/ContentsFiles/VT50_BiasAdjust.pdf
VT50 wiring Schematic
http://www.audioresearch.com/ContentsFiles/VT50_SchemPL.pdf
Three trim pots are found behind the side panels on the right and left side of the amp.
I recommend meter leads clip on hook probes be used for making the necessary adjustments. Be careful, lethal DC voltage inside. Not to mention the damage that could be done if a probe shorted across a power trace.
Jim
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Yes, I for one remember seeing Abe Collins' great step by step presentation for re-tubing his VT100 amp back in 2005. I also remember him saying the process was a real pain in the butt. LOL, I should also add Abe got rid of the amp long before it needed re-tubing the small signal tubes again.
>>>>>>>>>>>>>>>>>>
For those of you that may have an ARC VT50 amp and didn't know the 6922 tubes needed to be biased.......
The VT50 is relatively easy to bias the 6922 tubes PROVIDING you start with tubes with closely matched triode sections. If the 2 triode sections of each 6922 tube are not closely matched you will/could spend hours switching the tubes around to get the closest possible plate voltage measurements for each 6922 tube and still not get the best possible results. Especially the driver tubes. So save yourself a lot of time and make sure you buy from a vender that can deliver dual triode 6922 tubes with closely matched sections.
A little back ground. I bought my VT50 new in 1997. No where in the owners manual does it say anything about the need to check and re-adjust the bias voltages on newly installed 6922 tubes. I have re-tubed the amp 4 times now and up until this last time never biased the 6922 tubes. I would just replace all of the tubes each time. The only tubes I was biasing was the power output tubes. I guess I have been lucky. I have never read a post on any audio forum about biasing the 6922 in a VT50 either. I have read tons on the VT100 and VT100 MRK 2 though. Blown resistors and all.
A couple of months ago I ran across the ARC PDF for biasing the 6922 tubes in the VT50 as well the wiring schematic for the amp.
So anyway,.... for those of you that may be interested.......
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