Comments for page: A New Look

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Posted by Dave April 21, 2013 - 12:08 am
Hi Pete -- I obviously missed your post here, so you have my deepest apologizes!

Ah, yes. Fisher's alternate DC heater supply! EFB(tm) is entirely appropriate for the output stage of the X-100, but the problem then is, how to power the small signal tube heaters. Basically, an alternate source of power would have to be provided since those tubes would not be powered by the output stage anymore. While that would complicate things somewhat, the effort would still be very worthwhile, as installing EFB would make a huge difference in this amplifier with regards to (at least) output tube life, since in stock form, the output stage has to conduct enough current to power the heater string, as you well know. By comparison, since the power amplifier section of the X-100 is similar in design to that used in the 400 (minus the heater string issue), you might check out my recent power amplifier rebuild of that unit over on the AK Fisher forum to see just how beneficial it was to add EFB to that unit.

I have two new universal EFB boards that should be available hopefully around July, one of which would work well with your amplifier. That would greatly simplify the effort to install EFB, but the small signal tube heaters will still need an alternate source of power. However, I believe that Radio Shack carries all the parts you need to make a small power supply to handle that job.


Posted by Pete M. April 01, 2013 - 12:35 pm
Hi Dave,
Great article but can this be done on a Fisher X100? It uses the cathode currents to run the preamp tube heaters. Perhaps an alternate plan could be devised?
Thanks, Pete

Posted by joe w. March 30, 2013 - 12:25 am
hi guys 7247 tubes are new from russia with love lol, god love the russians.

Posted by Dave February 25, 2013 - 11:20 pm
Hi Ken --
The process is underway even now. I am awaiting delivery of the first board -- that being the SCA EFB power supply board. They are slated to arrive around the end of the month. I am currently in the process of setting up the retail site to facilitate their sale, but see no reason why at least that board should not be available some time next month. Going forward, I would like to try and add an additional board every month until all the SCA and ST boards are available.

As for modifying the boards, of course, the SCA-35 power amplifier boards are already properly engineered to use 6GH8 tubes in the driver position. As for the ST-35 boards however, I know of no readily available tube that could be substituted, while still delivering the performance of the 7247/12DW7 used in that amplifier. Multiple tubes could be used to replicate the original tube, but space on the boards is just not permitting of this approach.

Ultimately, the boards basically have to be taken for what they were intended to represent, which is a very high quality modern replacement board for the original product, with common sense improvements (i.e. the conversion to use a 6GH8) made where practical.

Thanks for your interest. I'll post here as soon as the first board has arrived, and a definite date for sale/price can be determined.


Posted by Ken Parsons February 22, 2013 - 01:56 pm
Hi Dave,

I have just come up to speed re the discontinuation of AR and while oddly saddened, am very pleased that things will move forward through Tronola.

I and am interested in SCA35 and ST35 boards for both new projects and a current repair.

Per emails with George at AR I understand that they may well be in the works.

Two Qs;

1) do you have any time frame?

2) is there an argument to be made to slightly modify the board designs to incorporate current production signal tubes vs the 7199 and 7247 used in the SCA35 and ST35 respectively, given this new direction for replacement board production?

(I appreciate that the 7247 can be bought new, but only from JJ - perhaps all fine - but a wider set of alternative might be useful, tbd)

Thanks a bunch

Posted by Dave February 08, 2013 - 07:24 pm
For the many who have contacted me privately, as well as those who have publicly inquired, I would like to give an update as to the future availability of boards containing the EFB(tm) modification.

With the recent closure of Pacific Audio Regenesis, not only did that event bring to a halt the availability of high quality power supply boards that included on-board EFB for the small Dynaco amplifiers, it also terminated a source for all the other high quality replacement boards that company offered for many popular pieces of Dynaco equipment. The proprietor there, George Ronnenkamp, was a fanatic about every detail of his boards from their basic design and manufacture, to the components used, to a board's ultimate assembly for sale. He personally built and tested each board sold, allowing AR to achieve a level of quality and value that were second to none in the diy and restoration audio community. AR will truly be missed by a great many of us. Out of the ashes however, new possibilities always exist.

To that end, D Gillespie Designs has been granted exclusive rights to produce AR products going forward. These will not be assembled boards, but bare boards as originally developed at AR, virtually identical to the original, and manufactured to the same exacting detail and quality levels as produced for AR. A BOM will also be provided, allowing the purchaser to then obtain the exact parts required, with parts available from dual sources for completion. Some skill will obviously be required to assemble the boards, but with reasonable attention to detail, the vast majority of solder slingers out there should have no trouble producing a working copy of an original board. While this approach does not offer the AR convenience of fully assembled boards, it does allow for the basic boards to be available once again, such that when populated with parts from the BOM, can result in a very economical and workable solution for most folks.

The ultimate goal is to -- over time -- make available all the audio and EFB power supply boards for the SCA and ST35 amplifiers. Also in the works, are two new universal EFB boards that would have a very small footprint, which will allow the installation of EFB in virtually any vacuum tube amplifier or receiver out there that can benefit from its operation.

Pricing has not been set yet, but when available, will be offered and sold here on the Tronola website. The first board to be offered will be the SCA35 EFB power supply board, a production order for this board having already been placed. I should receive these by the first of March, to be offered for sale sometime later that month.

A huge tip of the hat to AR for creating such high quality products, and allowing their production to be carried on in streamlined form. Stay tuned as more information becomes available!


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