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In Reply to: RE: Futterman Story w/ Ted Hammond posted by rhinohifi714 on July 18, 2012 at 21:35:39
Hey Rhino I was hoping you might have a minute to answer a question or two regarding the JJ EL509 conversion on the H3aa OTL's.
Do the amps retain the original circuit design and just replace the output tubes? I am fairly familiar with the JF circuit from various rebuilds of H3's and NYAL OTL 1 & 3 rebuilds I have done in the past. Knowing that the original H3 circuit used many different tubes that had similar parameters as the JJ EL509's I am wondering what you did with those amps to make the switch? Less voltage? Reduced current? A completely new circuit?
Thanks Rhino for any info you might help with.
Follow Ups:
I don't know anything about the circuit design changes, but at some point George Kaye was offering to modify NYAL amps to use EL 509's. However he stopped doing this because (he told me) that the 509's he could get did not perform adequately.
Fortunately 6LF6's seem to last a long time...
Thx but I think the EL509's shown in the pics posted by Rhino are JJ Tesla EL509 which are different then say the Amprex version of the tube. GK was doing the Amprex tube version (max current to pass 1.4A). The JJ's pass 700mA max. Now I tend to think its not that big an issue as the early JF OTL's such as the H3 used tubes such as the 6HB5 that only passed 700 to 800mA but just wondering is Rhino could chime in here and offer up understanding on this???
Thx
A
Hi Anthony,
as far as changes to the original circuit in the h3aa and the 509s version pictured there are several, and I only know a few, the addition of pots for alignment as in the otl-3's was installed for easy alignment, as well as hexfred diodes, several bypass caps on both power and speaker caps. also bypass caps on the 4-way bridge rectifier. but that's all I know, I have only played the amps a few hundred hours since I got them from Ted, I had planned to take them back to Croton and he was going to go over all the mod's with me. There is no complete schematic for that amp, only handwritten notes concerning the changes.
Since then Ted has been undergoing chemotherapy for cancer off and on for the last year and a half. Hopefully when he gets better I'll get copies of the changes.
Concerning the 509s tube:
I was there when Ted performed max output at clip, the amps put out 95 watts into 8 ohms, so as far as them being up to the challenge in that design they appear to work ok. One thing I noticed though was when doing the alignment that I was near the max settings to get the 300 ma idle current recommended in the procedure, I think that may be a sign of the lower factory spec on the tube. When I tested the tubes in my Amplitrex to the same setting as I use on the 6lf6's they all showed to be considerably low compared to good 6lf6's, the problem is that all I have is the tubes in the amps and 6 spares. I think that there is a chance that they were just off the shelf tubes not premium examples.
There is a seller on e-bay that I contacted who said he could match sextet's of them and would guaranty they met the factory spec for mutual conductance, I need to make sure he is testing them using fixed not autobias settings to achieve those numbers.
Not sure I told you anything that will help you out.
Thx Rhino,
Greatly appreciate all your time!!!!
Thx for the update on Ted's health. Please wish him all the best from all of us and I am sure we all understand how a guy like himself has been so helpful to the hobby!!!!
So I understand you correctly could you please let me know if the EL509 tubes are 8 pin versions or 9 pin version?
Reason I ask is that the 8 pin version would be the JJ Tesla EL509 tubes which is what they look like in the picture you posted. Also in that picture one is missing and it looks like the socket is an 8 pin socket. Could you possibly clarify?
Thx again!!
It is an octal base, JJ el509s, the tube missing is one I was testing.
Good Eye.
Thx Rhino,
I think that explains the difference on testing you are seeing. 6lf6 1.4A, JJ EL509 700mA MAX! Could be wrong on that but that is just my guess.
I was wondering when you do the testing and amp alignment are you still adjusting to the voltages JF gave for the H3AA amp in his testing and Alignment papers? Or are the voltages different now that the output tubes are different?
My guess is no, meaning you are holding the original JF voltages...
Would be interested to know.
Thx
Ted said Julius knew what he was doing, yes original voltages were observed, 300ma idle current. 85v bias.
I can't argue that.
Hi, I would really like to send you a note on this topic, but it is of commercial interest. Let me know if I may contact you via email? I see you do not accept direct email messages.
Here is the second page for those who are interested
Thx Again Rhino!
I have uploaded the test socket voltage measurements sequence from JF. Are you getting a measure of 360V at the test socket as described in number 1? Also are you getting the 180v measurement at the test socket as described in number 2 & 3?
Your 85v front end measurement is lower then the JF papers I have so I was wondering of the other two measurements.
Thx again!
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