|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
24.247.173.245
In Reply to: ARC VT-50 + AI Modulus 3a = WEAK BASS...help! posted by tube lubba on September 16, 2004 at 12:58:43:
I tried to call ARC but they are closed on Fridays right now. The input and driver tubes may need to be tweaked. There are three tiny trim pots on the back of the circuit board under the side panel of your amp. It is my understanding that if these are not correct the amp will not sound or opperate right. If you didn't get the 6922's from ARC this might be the issue. I am going to get them to send me the procedure when I can get ahold of them. You seems that you just can't slap any old 6922 into the amp and make it work. It looks a bit tricky as the stuff is very small and you need to know what you are doing so you don't fry yourself. I will look into it a bit more.Take a look at this link. It is about the Vt 100 mkII which is the same as your amp with half as many tubes. I got this from a post by another AA contributor Abe Collins. (Click on the pic to go to the next page.)
Follow Ups:
I called the tech that worked on the unit and he did not even know the adjustments existed.
Glad I could be of some help. It's a well kept secret I guess. I wasn't sure of it myself until I took the side cover off my amp. I was aware of it from hearing about this on the 100 and figured it would be similar. There should be something in the manual about this but there isn't. I guess they just don't want to scare people and just sell them tube sets.
I just popped some old GE 6550s in there and it has more weight already (20 min). I will order the wing c 6550s.What are you using for the input and driver tubes? when I get all the tubes together I will have it biased professionally.
Oh man the 6550s make a difference!!!!!!!!!!!!!!! un freakin believable.
I plan to put the Electro Harmonix 6922 gold Pins in, They sound so darn good in my ARC pre amp. I am using the Winged "C" (S.E.D/old Svetlana) 6550's. It's coming up on time to replace mine. My amp was one of the last ones made so the tubes are still not all that old.Did you re bias the amp for the old GE 6550's?
Once you get everything running up to snuff you will love that amp! Perhaps with the drivers adjusted right you might like the KT's, but my gut feeling is that it sounds SO "right" with the S.E.D's I can tell you for sure that they do work very well.
I have a friend who owns a VT 50 and an LS 7 that I put an IEC on and swapped out the cheesy yellow REL caps for DynamiCaps. That combo sounds great
Keith,
These Ge 6550's are unbelievable. the guy sold me the amp with the kt-88s almost new (now about 100hrs). I just popped the nos ge's in and within a half an hour it was a completely different amp(he gave me those too). No adjustments. The EH 6922 are in the dirver and input without adjustment either(with rings).
TTYS, jay
I willmcontact the gentleman that I purchased the amp from and the technician that he hired to bias the tubes. Maybe the work was not done correctly.It is probably best to sit on things until Monday. I agree that it is a good idea to contact ARC. I really dont feel comfortable making adjustments on the amp so I will probably have to pay someone to do it.
The main question is: should the amp be adjust it with the Electro Harmonix tubes that are in the unit or should I just start from scratch with new tubes?
Hopefully the inverted phase output of the AI modulus is not an issue either. I will confrim that with ARC.
Thanks for all the help so far. I am very excited to get this operating properly.
I do feel that the S.E.D. 6550 will make the amp perform the way it was intended to. The EH 6922 is a great sounding tube and if you get the rail voltages right would be a keeper. The KT's may work better with this done. Something isn't right if you don't like the bass on that amp as the bass is one of it's many qualities that are amazing.My bet is that within it's power range it holds it's own with the REF series amps as far as beauty of sound.The manual makes no mention of this adjustment so the previous owner or the tech may not have been aware it needed to be done. Most tube amps like your VT60 you can just plug in new input/driver tubes, bias the outputs and fly without this. He may have had other tube amps in the past and assumed that this could be done. If you buy tubes from ARC they may be able to send you 6922's that plug right in as they have matched them and done some measurments, but I'm not sure of this at this point.
My friend got his VT50 used from a guy that used it single ended. When he got the amp there were no jumpers for the XLR's for SE opperation. When he asked the guy where they were he didn't know what he was talking about. WOW what a bone head. It's no wonder he sold it. Wec got some from ARC and all is as it should be now. The amp is a small wonder. Don't give up on it. I will never give mine up!
Good luck and let me know what you end up doing.
To fix the polarity just reverse black for red on one end of your speaker wire. It's too easy.
nt
This post is made possible by the generous support of people like you and our sponsors: