Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
In Reply to: RE: MP Engineering OTL posted by Kasanay on June 02, 2016 at 14:16:47
Without a schematic, diagnosis would be very difficult, but I bet this is a Futterman-type OTL. What are those output tubes? Are they 6LF6s or related? They are really close together, too close. One clue would be the presence of an output coupling capacitance; are they cap-coupled?
They look home-made or else you've taken off a cover to make the photo.
These are very similar to the Futterman H1.
Tubes are 12B4A (same as H1)
The amp uses capacitor coupling. Currently they are big 4uf oil caps. I am planning to replace these along with the electrolytics in the very near future.
They are not quite home made. They were made by MP Engineering of Fairfield Conn. - a small company that was in business for 30 years. I did remove the access panels.
They don't look like 6LF6's since there is no anode cap. I found a thread on the web which says they are 12B4A tubes, and (further down) that this is a "best kept secret" tube. Someone on the thread claims to have a set of schematics for them.
Here is the link:
Didn't Julius use those in one of his earliest efforts, before he went to the 6LF6?
It is my understanding the early Futterman H1 used 12B4As.
These amps are very similar.
He might have used them also, later, as output tubes in his headphone amplifier. During one of my two visits to his shop/factory in NYC, he was building a headphone amplifier that he proudly showed off to me. It had smallish output tubes with no cap lead. I know someone who owns one, and we speculated whether his sample was the one I looked at in 1979 or thereabouts.
I have no idea. Rhino, do you know?
Post a Followup:
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: