|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
24.13.177.16
In Reply to: RE: NYAL OTL 3 posted by Lew on November 18, 2010 at 11:44:31
I alway saw this variability (in [trans]conduction?) in my OTL3s
there were issues with getting (overpriced) tubes
and rarely ever matched one another.
My tubes would routinely pulse... purple.
I think that Ralph (as typically is the case) is correct
that some tubes under a dynamic load draw more
that others in the circuit.
The AS M60 (in background) was the best solution...
Follow Ups:
Hi,
I was not able to do much on the amp as I had been busy with other matters, however I managed to obtain some 6LF6 tubes from ebay in the meantime. Today I replaced the tube with the orange glow with 3 new tubes in turn and each tube started to also glow immediately upon switch on. Does this indicate something. I doubt it is a tube issue. Comments would be appreciated. Thanks.
Nara
Hi,
Need to revive this thread as I still have not resolved the issue. To recap:
VI developes an orange glow upon switch on. It is similar when moved to V2 and V3 position. V1 is OK in V6-V8 position. V2 and V3 are OK in V1 position. V6-V8 also glow in V1-V3 position but are OK in their original postion. In addition to the glow the affected tubes get extremely hot.
I have since purchased 10 6LF6 tubes but each has a similar problem in V1-V3 position.
Have not attempted biasing in view of the overheating.
Inputs on what could be wrong would be appreciated.
As a last ditch measure, am considering converting the amps to OTL 3Q as I would then need only 4 6LF6 tubes. The lower power output is OK as dont need much power to drive the Tannoy HPD385(8 Ohms, 91db), previously driven by late Geroge Wright's 2A3 monos (3.5 Watts).
Assistance from members would be appreciated.
Thanks and Regards,
Nara
Hi !Remove and check all trim pot`s with ohm meter , one by one , but without turning trim pot sliders .
I`m suspect that Amp upper bank of power tubes which plates glow orange have no correct G1/G2 bias beacose of bad bias trim pot .
Sign of incorrect power tube bias is that you don`t have exactly 1/2 of V1,2,3 B+ plate voltage on the lower bank of power tubes plates .
For example :
If you measure +300V on the upper power tube plates (V1,2,3) terminals than you have to measure exactly +150 V on the lower power tube plates terminals .Best Regards !
__
Enlightened Evolution-Astral Projection
Edits: 05/23/12 05/23/12
Thanks for your comments Banat. Only 1 of the top bank of tubes glows. If there is an issue with the trim pots, should it not also affact the other 2 tubes in the upper bank. Yes I would check the trim pots anyway.
As a last ditch measure I'm seriously considering converting the amp to the 3Q version with only 2 tubes in the upper and lower banks respectively. Would like to seek inputs from members on what other changes if any that need to be made to the circuit other than just removing 2 tubes. If I am not wrong, the photo in Mike Mounts post shows the OTL3 Q. Would Mike like to confirm and comment please. Comments from others using the 'Q' version would be appreciated
The few comments on the OTL3 Q that I have read, state that 1 tube in the upper and lower bank are removed and capacitors added to roll off the base at @100hz. The capacitors bit would not apply as I would not be using the amp to drive the Quadb
Rgds,
Nara
If only one of upper bank three power tubes glows than check the value of G1 grid stop resistor on that glowing tube first , since that grid stop resistors is only non common element of upper power tubes bank negative bias network , but is separate for each power tube , check for bad solder points around that glowing tube socket to .
BTW , NYAL OTL 3 is not very complex electronic unit and some factory service manual which include voltage and current chart , adjusting points ,... etc , well be very helpful for quick service and quick malfunction diagnose .Best Regards !
__
Enlightened Evolution-Astral Projection
Edits: 06/05/12
Thanks for your comments Banat,
Checked all the resistors when I received the amps and they were all within specs. The problem is not with a particular tube position in the upper bank.
Only 2 of the original tubes in the upper bank do not glow in any position in the upper bank. One tube in the upper bank glows in all the 3 positions in the upper bank. Also all the 3 tubes from the lower bank glow in all the 3 positions in the upper bank. All the six tubes do not glow in the lower bank.
Also all the 10 tubes that were purchased subsequently glow in all the 3 positions in the upper bank. Frankly I'm puzzled. If the problem is with a particular tube position in the upper bank,then it would be easier to find a solution.
This is the reason why I am considering using the amp with 2 tubes in each bank if this does not require any change to the circuit.
Rgds,
Nara
How much plate current are you drawing? Lift the positive leg of the bridge rectifier and insert a meter, if you are over 500ma dial it back to around 350, sounds like you are running them too hard and the ones that do not glow can withstand the high current and the glowing tubes cannot.
Buy a set of tubes from Roger Modjeski, (ram tubes) they are the best you can get.
Hi 714rhino,
Thanks for your reply. To date it appears to be the most appropriate solution to the problem with the OTL3.
Would like to check with you, instead of lifting the positive leg of the bridge rectifier to measure current, could I set the current (350mA) and center balance by adjusting R16 and R23 as indicated in para 9 of the biasing instructions.
Thanks & Rgds,
Nara
Sorry not to get back with you sooner, I will send the alignment procedure to your e-mail tomorrow.
Thanks 714rhino but I do have a copy of the instructions. I am not up to it to bias the amp and would be getting a tech competent friend to do it for me soon. I was just wondering if in the meantime I could just set Ip and balance as indicated in para 9 of the instructions and see if the glowing stops.
Rgds,
Nara
Do the full alignment procedure as described in your manual, if you cannot get the amp to align properly you know that there is a problem either with the tubes or a passive component causing a problem, cap/res...etc.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: