Fairchild 660/670

[mossboss]

Hey all
Has any one here built the "Poor mans" version of this compressor limiter as per DIY Prodigy by Analag and Silent Arts?
I am looking for some feed back on the project as I am in the process of getting one or two happenning
We are already well on the way with a 670 version
A fair way to go yet as TIME is the enemy at present
There are a couple of builders located in Aus but pm's to them has yet to yield a response
One is having issues with the power supply the other has posted little or if he has I am not aware
By the way there are around 90 odd pages on the first support thread and another with about 30 odd pages
It seems that most issues arise in the power supply department
Any input on this build from any one here would certainly be welcome
Once it is done (with some mods of our own) it will be made available for a few weeks for people to give it a work out so as to get some real life feedback
We are going for a full valve power supply as well as valve bias for the grids as against the solid state version that is included in the original design as well as a higher output stage to get closer to the original Fairchild specs
The attenuators are switched over 21 or 22 steps rather than just pots
There will be a choice as to the as designed compress attack time base or switch over to the original times on the Fairchild design
It will also take around 8 odd slots in the rack and weigh around 1.5 bags of cement Lots of Iron in there
I am not so sure as to the terminology of "Poor mans" on this as it has cost a fair amount so far and it will eat some more hard earned $
I suppose in relative terms it may be based on the fact that at around $30K odd for an original Fairchild 670 spending a couple of grand plus to build a close clone you would have to be in the poor man's category
By the way there is another clone that has just being released by drip electronics that follows the original specs and design steps
Looking at that as well as the next project!
The transormer set alone runs at about $2.5 K aussie and the valve set around another $1000 so it will fall in the category of not so "poor man"

The specs published so far by Gregory seem very impressive the design also well thought out
I guess around the $7,000 K odd will see this beast glowing in the dark in someones rack plus his time and effort, Arghhhhh Time Time Time
Here is a link and I am not on a commission either http://dripelectronics.com/660.html
Cheers

[Mac]

Hey Chris, Best of luck with the build. Thats about 20 more tubes and 10 more transformers per box than I am used to working with!!!

EPIC...

One day I shall rise to this challenge....please do post photos of your journey into this. I, and I am sure many other will watch with interest.

Mac.

[mossboss]

Update
One of the Aussie builders did contact me He has finished his poor mans 670 with some mods already posted up on the "pimp" pages by a frenchman. diy forum member, going by the nickname of LoLo and he is really happy with it
He is a pro with a recording studio in Vic
He has already invited us to go and listen to a live take with it on line
Great response so that is a good thing
Will provide some feedback here after the "subjective" listening session has taken place on this unit
By the way the mod's do follow the original Fairchild time base
Itll be interesting
Cheers

[Barney Loveland]

I have boards and audio transformers but am yet to get to this one. Have a few other things brewing, will post when done.

[Chinagraf]

Where are the 6386's coming form? Are they the new release ones someone is selling?

[mossboss]

Hi
No 6386's on this one
On the input there are 4 6bc8 or 6bz8 valves
Second stage output that is, there are 4 x 5687 valves
The design philosophy is the same as in a Fairchild
It is closer to the Altec 436 which uses the same input variable mu valves with variable attack/compress control on a side chain that the Altec lacked
By the way the localy made AWA G54639 Limiter supplied to most early days radio stations around Australia is of similar design as the Fairchild using 6ba6 and 6v6 gt valves as well as 6au6's
I think that once the cat was out of the bag everyone around the world chased it when you consider that the 660/670 was designed and originaly built around the early fifties and not by Fairchild first either the concept was taken up by more than one maker around the globe
When you really look at the design it is no more than a transformer coupled tuned mixer quiet a common design in any radio transmitter from the late 20's on
The man had the vision to apply it to sound limiting compressing primarily for radio stations so as to stop the things blowing their output valves even if some of them where around the 15-20 KW
The drip design uses the Slovakian made new 6386 at $125 US a pop but this Drip electronics clone is the closest I have ever seen to a Fairchild unit using the exact componentry but on a pcb rather than point to pint
By the way I did see a set of 4 NOS 6386 going for $500 EACH
It is the unobtainium substance coming into play
Further if any one will tell you that the 6386 would do more than around 500 hours ON on a Fairchild he is having you on That is a very short time for a tube but they where driven hard in the design so there is little NOS around as they got "cooked" on these things besides other devices used this particular valve as well,
It was a rather specialised tube with the grid wound on the post in a variable pitch type Like a spring that it got stretched unevenly with the windings more apart towards the top of the valve therefore Variable mu
Never the less Due to low demand it was never made in large quantities and by not many manufacturers since it was never taken up into any JAN procurement which requires at least 4-5 manufacturers be able to make any component
Any way this is the "poor mans" version and with the pimps feedback so far is extremelly positive
Cheers