Subject: RE: Who done it?  Philbrick Amplifiers.

Date: Thu, 3 Mar 2005 10:18:08 -0500

Thread-Topic: Who done it?  Philbrick Amplifiers.

From: "Sheingold, Dan" <>

To: "Robert A. Pease", Joe Sousa, Dan Sheingold


Wow! I'd forgotten half of these! Trying to peer through the clouds, I'd guess you were at least 90% correct on most of the stuff I remember.

I'll just insert my (few) comments in square brackets.


-----Original Message-----

From: Robert A. Pease 

Sent: Sunday, February 27, 2005 6:14 AM

To: Joe Sousa, Dan Sheingold, Robert A. Pease

Subject: Who done it? Philbrick Amplifiers.


  Hello,  Joe  Sousa, I will try to  define  which guys  designed  WHAT old   Philbrick  products. As far as I can. 

But  before you post this,   you must get approval from Dan Sheingold. If Dan and I agree, you can post it on your web pages. 

If  Dan is not  sure,  or  if  I am not sure, we might ask Bruce Seddon. But Bruce is  very busy this month, moving to Vermont.   If there is  an  item  and we are not sure, you could post it with a big question mark.  Does that seem fair, Dan?


PRELIMINARY list :   First  Draft. 


(Power Supplies)

 SR-400  -  Roger  ("Tim") Noble.  

 R-100A -   Tim Noble?




 R-600  -  all  4 engineered by Bruce Seddon. Many are working reliably in 2004.

K2-W -  designed  by George  Philbrick AND FRIENDS.   ( Per text  by DHS)

K2-X -  ? George Philbrick  and/or Roger "Tim" Noble. ?  [Used 6AN8. The plates glowed a pretty red under load]

K2-XA - redesigned  by Tim Noble  using  6BR8A and bootstrap bias for the  Neons, about 1961 K2-XA - redesigned by Tim Noble using an NPN follower, to hold the Pentode's Cathode at -120 volts.

       About  1962.  This  version is ~ 2 x slower than the earlier

K2-XA.  * See RAP's column.

K2-P -  Chopper-stabilized] [ing] amplifier - by  GAP  and friends?

K2-PA  - a version of the K2-P with slightly revised grounds. [Probably Bruce Seddon]

K2-B-  Booster  -   designed by - ? [George? Tim?]

    *** CAUTION, the  filaments  should be  biassed at - 150 VDC, or the tubes  may  become unhappy  and set fire  to the whole  assemblage.

K2-cases  that are black or  yellow-brown are NOT fire-retardant. [Also not safe against shorts to ground]

*  K2-WJ

*  K2-PJ

*  K2-YJ

*  K2-BJ   - all engineered by Bruce Seddon.   Military versions,  built on  terminals on PC boards (rather than the K2-W's  rats-nest.)  These used mil-type tubes, and  used no Neon lamps  (which were unacceptable due to radiation prohibitions  in some military projects such as submarines) but instead used zeners. [The neon lamps needed ionizing radiation to ensure reliable starting, originally provided by radium paint, later by lamp manufacturer (GE) incorporating traces of radon gas. NE2 became NE56 (58?)]


(((" K2-J"  - never  sold  by Philbrick. This was  a version of  Loebe Julie's 1942 amplifier,  with positive feedback added to bring up  the gain from 2000  to 30,000.  One was  built by RAP in 2003, using 6SL7GT's.  Just  a half-baked idea of RAP. )))


USA-4   - Bruce Seddon. [There was also a military version, USA-4JX, see p. 10 of the Applications Manual]

USA-3  -  George Philbrick AND FRIENDS?   Did Bob Malter help? It looks like some of his ideas. 

[The first version of the "Universal Stabilized Amplifier" I ever saw, on a narrower board, was George's USA-2 design. Bruce and Bob redesigned it to be manufacturable and work properly, and--because it needed a larger form factor--called it USA-3.]


SK2-V (+/-  100 volt output using  12AX7, 12AU7, and a matched pair of 6CW4 Nuvistors, in Walter Kern's  metal package) SK2-P - Chopper-stabilizing amplifier  (in Walter Kern's  metal package) SK2-B - Booster using 7119  triodes. (in Walter Kern's  metal package)

   ***     The basic design of these 3 amplifiers was by GAP (and friends)  and optimized and put into production by R.A. Pease



 P7 - researched by George Philbrick, but he  never got it into running order.   **

 P2 - designed  by Bob Malter, and put into production ~ 1961.  Very valuable and very profitable.  **

**  Refer  to the  Chapter in Jim Williams' book on this subject. I am sure we can get permission to put this on  the web-pages.  

P2A - when the  production of  2N384-type  germanium transistors was stopping, about 1968,  George Philbrick designed the basic P2A, using silicon transistors.

     A very finely optimized design. I helped  on some of the frequency compensation, and production engineering. 


SP2A  - a plug-in version  of the P2A, in  Walter Kern's SP  package.  RAP's layout.

SP2B -  a 20-mA version of the  SP2-A. The  20-mA booster went on a mini-board.

SP102 - a  +/- 100  volt  redesign of  the SP2A.  All the  RF amplifiers ran on the same 1mA, stacked up in series. Slightly ingenious.


*** The  above  amplifiers  were RF-coupled (5 Mcps).  Below  are the ordinary DC-coupled  amplifiers.

P65  (also known as 6141) -  Alan R.  Pearlman   - ARP.   6 transistors.

PP65 -  George Philbrick's  layout, a potted  module, after ARP and Tim left to form NEXUS - George designed the package, in  co-ordination with Walter  Kern.

P65A  and PP65A  -  a souped up version of the   P65, to 2 mA  output. 

Probably  a collaboration of RAP and George Philbrick.  It was  feasible because the 2N1132's beta  was improved from 7 min....


 The  6151- or - P75 - ARP.   (Darlington Version of P65)

****   (I'll be happy to let ARP  explain why HE and  Sidney Darlington invented the  Darlington at the ~ same time -   but Darlington  published first.....)  (If you have any \ trouble getting that story out of ARP, I'm willing to help.)  It's great history.


 P25A and PP25A   -  RAP's  work; a   FET  version of the P85.  Using  Amelco's  FETs  (NOT matched  by Amelco, but  matched by GAP/R)   that had 1500 Umhos at 300 UA.  Good Ig, better than 150 pa.  One of the first good FET-input amplifiers.  The PP25A  was potted in yellow  epoxy.


P85A  and PP85A  -  RAP's  work  - high CMRR  redesign of  P65, using   8 transistors. See also P25A.

RAP  did the PC board   layout on  both P85 and PP85.  P25A and PP25A used the same  PC boards as the '85's.  The PP85A was potted in red epoxy.

P35A and PP35A  -   John I. Smith's design, a complete redesign of the 

P75.  It used FETs  in the second stage, to give better drift and stability.  A nice improvement.

Grey epoxy?

P55A, PP55A - a downgraded  version of P65, with  lower beta

input-transistors.  Looser IB specs.

P15, P95 - no such animal!  Never existed, never built.  I never heard of any such thing proposed.

  (But think of the  fun we could have!)


PP25AH  - a discrete-component version of the Q25AH.

PP85AH  - a discrete-component version of the Q85AH.


Q25AH - a small hybrid  op-amp with  about  12 transistors, assembled to Philbrick's specifications by Amelco Semiconductor (Mt. View CA)    The inputs were well-matched FETs  driving a diff-amp. In a  12-pin TO-8 package - about 0.6"  diameter. RAP's design.

Q85AH  - same as Q25AH, but with  NPN  input transistors, instead of

FETs.  "Microhybrid" .


T52 -  same as Amelco 809BE.  RAP's  design, Philbrick's first monolithic operational amplifier.

T82AH - Same as Amelco 806BE; Not  RAP's  design.


P45 and PP45  - RAP's design, to do 100 MHz  Gain-bandwidth  product.   +/-  20 mA output.

RAP's  layout.  It used an NSC  "134P2"  PNP, Similar  to 2N2604.  PP45 in dark gren epoxy.

P65AH and PP65AH - high-speed version of P65, using  2N2907, rather than 2N1132. 

 It had  27  MHz  gain-bandwidth  product; but it was  not  purely symmetrical.  (Neither was the P65 or P75). Details   available - later.   RAP's design. 

P65Q  and  PP65Q - a micropower  version of P65,  drawing less than 0.9mA Iq. Output drive, +2, -0.5 mA.  RAP's design, using high-beta 2N2907. I talked George into it.

LPP65A -  low profile  potted module, cut from 0.625" max to 0.5" max height.  TO-5's  were thrown out.  The 2N2907 (TO-18)   was much smaller.

LLPP65AH -   a very low-profile potted-module version of  PP65AH, about 0.22" high. Built with "Moly-Tab"  transistors.  I think I built only ONE.  (But it was 



"U"   such as - "P65AU,  PP85AU, P2AU" -  MANY  of the  products listed above could be made with  plastic or  epoxy-packaged  transistors.  Not all were, but  

many were, and if a customer had  enough VOLUME,  he could get almost anything made with epoxy transistors....


SP656 - a  chopper-stabilized  amplifier using  PP65  and  a transistor preamp, mechanical chopper, and  a 20-mA output stage.

SP456 - same as above, but using a PP45  100 MHz  main amplifier.

SP656-P-  version of SP656 using a  photo-chopper.


Solid-State Power Supplies:

PR-150  - Tim Noble.   It had  mediocre start-up, and poor short-circuit protection, due to the use of mostly germanium transistors, and an imperfect design.

PR-300 -   to replace the PR-150. Designed by John I. Smith (with comments  from Bob Malter)  All-silicon.  Solid as a  rock.

PR-30 - a  little joint project with   - Bob Malter, Dan McKenna, RAP?  

Reasonably reliable (Unless short-circuited for a long time.)

PRH-120 - RAP's design, to put out +/- 60 mA at  +/- 120  volts, for  various hi-voltage boosters.  Built into the PR-300 package.


THIS  is not any complete list of Philbrick Amplifier Products, and it 

is NOT a perfect list of WHO designed WHAT.  But it is a good start.



Who designed all the Nexus Parts?  DA-1, SA-21?   We should ask ARP.  Many of these were sold by Philbrick/Nexus Research Labs.....   I am sure  many were  

designed by  the team of ARP and  Tim Noble, with  other collaborators.

 Who designed the 1009, 1011, 1026, ETC ETC ETC?  Let's ask Arnie Liberman.  He designed a lot of these, and/or  he would know who did.

K4-FF  function ["fitter"] generator.   GAP  plus friends? [FF had two rows of pots, one set to adjust 8 breakpoints, the other to adjust 10 incremental slopes. Of course the trouble with it as a function fitter was its discontinuities. George fixed this by adding adjustable high-frequency triangular dither at each break point, which produced parabolic rounding tangent to both adjacent slopes, giving a smooth curve. The points of tangency (and hence amount of rounding) were adjustable with dither amplitude in the FFR, a successor to the FF, with a third row of 9 pots.]

SK5-F   -  -  GAP  plus  P.D.Hansen  with production engineering  by Mayer E.Wantman.

F2-V   - 3D function generator  - - GAP plus friends.


Computing modules:

K3-A,-B,-C,-D,-E,-H,-J,-K,-L,-S,-T,-sigma,-tau,-V,-Z]; K5-U, SK5-U - -

GAP plus friends...

[There were two early series of shelf-mounted modules, the 1/4-rack-width K3s, and the rack-width K4s--including the K4-MU (dual) multiplier, the K4-FF], the K4-CO (P-I-D) controller, and the K4-DY (which incorporated a second-order differential equation)]

  Still not complete. But it's a good start. 


RAP's  OTHER  products, that he designed for  Philbrick Researches:


DACs? I designed the 4001  and 4002, Philbrick's  first  (16- and 14-bit  DACs) . I may have helped on other DACs, but  not  much.  About 1970?

V-to-F  converters:  4701, 4703, 4705,  4707, 4709, 4711, 4715, 4721  - all designed by RAP

F-to-V  converters:  4702, 4704, 4706, 4708, 4710 , (4722?)  - all designed by RAP.  About 1969-74? P and PP85C; P and  PP65C; P and PP25C - "compensated inputs"; details later.

P45AL and PP45AL - a 1-MHz  version of the faster P45.

Other circuits designed by RAP:  PT&H, PPT&H.   6628.1.  and - probably several other  bootleg products. ....


John I Smith's other  Circuits:  SPT&H. SP-FF Function fitter?   (NOT the SP-ARF)

All for now - this  has been a BIG project, just writing down all this history. !!  / rap