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Ehrhorn Technotogical Operations, Inc.

4975 North 30th Street

Colora o Springs, CO 80919

OPERATING AND TECHNICAL MANUAL

HIGH FREQUENCY LINEAR POWER AMPLIFIERS

MODELS PA-76, PA-76P, and PA-76C

EHRHORN TECHNOLOGICAL OPERATIONS, INC.

R vis d May 1, 1977

TABLE OF CONTENTS

SECTION 1

SECTION 2

SECTION 3

SECTION k -

SECTION 5 -

SECTION 6 -

ET0/"ALPHA"

- G n ral D scription and Sp cifications

■ INSTALLATION

High Voltag Tap S l ction

...............

Int rconn ctions With Oth r Equipm nt . . . 4

• OPERATION 5

Initial Tun -Up

........................

Op ration At 1 KW and 2 KW Input

.........

ALPHA 76P and ALPHA 7&C Op rating Diff r nc s 8

Op rating Not s

........................

Troubl shooting Hints

..................

THEORY OF OPERATION

....................

ILLUSTRATIONS

..........................

Transform r Installation or R moval . . . . 13

R ar V i w

.............................. 13

Top Vi w Showing Major Compon nt Locations . 14

Sch matic Diagram

......................

Front Pan l V i w

...............

Front Cov r

STANDARD ELECTRICAL PARTS

...............

PRODUCTS WARRANTY

...............

Back Cov r

EHRHORN TECHNOLOGICAL OPERATIONS, INC.

CANON CITY, COLORADO 81212

5/77 U.S.A.

Th ALPHA 76 (mod l PA-76) is a s lf-contain d high fr qu ncy lin

ar pow r amplifi r capabl of continuous op ration at d-c plat

pow r inputs of 2.5 kilowatts PEP for SSB voic and on kilowatt

av rag or continuous carri r with no tim limit (NTL). Th ALPHA

76 is tunabl ov r th rang 1.8-2.0 MHz plus 3_3° MHz, optimiz d

for conv ni nc in th six amat ur bands of 10 through 160 m t rs.

SPECIFICATIONS (Mod l PA-76)

Fr qu ncy Cov rag : 1.8-2.0 and 3-30 MHz (including 10-160 m t rs).

Plat Pow r Input; 2.5 KW PEP/SSB, 1 KW av rag or k y down, CCS.

RF Pow r Output: Typically 1.5 KW PEP/SSB, 650 watts carri r, CCS.

Driv Pow rs Nominal 100 watts PEP, 60 watts carri r.

Input & Output Imp danc s; Nominal 50 ohms r sistiv , unbalanc d;

VSWR 2:1 or l ss.

Distortion: Third ord r IM mor than 30 3b b low 1 KW PEP output.

Harmonics : Mor than 50 db b low m an fundam ntal fr qu ncy output.

Tub Compl m nt; Two Eimac 88?^ c ramic-m tal ground d-grid triod s.

Cooling: Full-cabin t, duct d forc d air; c ntrifugal blow r.

ALC: Adjustabl thr shold, n gativ -going standard as shipp d.

Prot ction: Primary fus s, plat ov rcurr nt r lay, AC and HV

int rlocks.

Primary Pow r: 24QV/10A or 120V/20A, nominal, 50-60 Hz.

Siz and W ight: 7.5"h. x 17"w. x l4.75"d. Shipping wt., 75 lb.

Optional Modifications Availabl :

Lightw ight Hip rsir^ pow r transform r r duc s

n t and shipping w ights by approximat ly 20 lb.

HI/LO (or "SSB/CW-TUNE”) tap chang r lay, front

pan l controll d.

Id ntical with PA-76 abov xc pt tub compl m nt

is thr 8874's, incr asing plat pow r input rat

ing to 3+ KW PEP and typical rf output to 2 KW PEP.

Do s not aff ct long t rm av rag or continuous

pow r ratings.

"Comm rcial" mod l id ntical with PA-76 xc pt

tub compl m nt is thr 8874' pow r transfor

m r is sp cial 2.4 KVA Hip rsir^, and option "R"

is standard. PEP ratings, d-c input 3 KW, typi

cal rf output 2 KW; continuous carri r or long

t rm av rag ratings, d-c input 1.6 KW, rf output

1 KW CCS (RATT, A0, tc.)

-1-

SECTION 1

GENERAL DESCRIPTION

Option "L" --

Option "R" --

Mod l 76? --

Mod l 76C --

Unpacking: Car fully r mov amplifi r and transform r from car

tons; SAVE ALL PACKING MATERIAL FOR RE-USE - SHIPMENT OF THE ALPHA

76 IN OTHER THAN FACTORY PACKING MAY RESULT IN DAMAGE NOT COVERED

UNDER WARRANTY.

Insp ct clos ly for vid nc of shipping damag ; if any is found,

notify d liv ring carri r and s ll r at onc . Compl t warranty

r gistration form and mail to ETO.

2. Transform r Installation; Th top cov r and th right-hand nd

pan l ass mbly of th amplifi r ar asily r mov d for transform r

installation. R mov th six flat h ad Phillips scr ws from th

top and two pan h ad scr ws from th r ar flang of th top cov r,

and lift it off.

To r mov th right-hand sid pan l ass mbly, r mov th two flat

h ad scr ws at th right dg of th front pan l, two at th dg

of th r ar pan l, and thr pan h ad scr ws at th dg of th

bottom plat . Pull th nd pan l ass mbly straight away from th

main chassis ass mbly.

Ori nt th transform r so that th two multi-pin, mold d plugs on

th transform r harn ss point toward th front of th amplifi r;

mov th corr sponding mating conn ctors in th amplifi r its lf

t mporarily out of th way (it may b n c ssary to tap or ti

on or both of th m out of th way whil installing th transfor

m r) . Car fully slid th transform r into position so that th

i-20 tapp d mounting hol s in its bas lin up with corr sponding

hol s in th amplifi r bas plat . Install th J-20 bolts and

wash rs provid d through th bottom plat , and tight n s cur ly.

Ch ck both pairs of conn ctors visually for prop r mating ori nta

tion (avoid xc ssiv harn ss b nding or twisting, as it may caus

damag to wir s or conn ctor pins) and mat th m firmly, pushing

until th int gral latch s ngag .

3» El ctrical Installation: If th amplifi r is to b us d with th

typ of a-c mains arrang m nt for which it has b n factory-wir d

(220-250V, 50-60 Hz, 1 phas , unl ss oth rwis sp cifi d) th nd

pan l and top cov r may b r plac d. If chang -ov r to 110-125V

pow r is n c ssary, mak th following chang s first:

Chang -Ov r to 110-125V Op ration - (Th amplifi r will op rat

normally on 110-125V, 50-60 Hz pow r if th primary supply cir

cuit is of ad quat capacity to d liv r th r quir d curr nt with

r asonabl r gulation (approximat ly 20 amps p ak, 5-10 amps av r

ag at full pow r, xc pt PA-76C up to 15 amps av rag ). To

chang from 220-250V to 110-125V op ration:

(a) Locat R4 (2000 ohm/12 watt r sistor mount d just abov th

RELAY jack on th r ar pan l); install a short jump r of #22

or larg r wir across its lugs, shorting it out.

(b) Locat th 9 pin transform r plug P2. Th transform r l ad

wir originally in th pin 3 position of P2 must b mov d tc>

th pin 2 position in th mold d sh ll? also, th l ad orig

inally in th pin 6 position must b mov d to th pin 5 hol .

CAUTION! DO NOT ATTEMPT TO REMOVE THE CRIMPED-ON PINS FROM

THE PLUG WITHOUT AN APPROPRIATE EXTRACTION TOOL AS DAMAGE TO

SECTION 2

INSTALLATION

PINS OR CONNECTOR IS AIMOST CERTAIN TO RESULT. On r qu st,

ETO will supply at no charg xtra push-in pins with short

l ads attach d. Onc th amplifi r is chang d ov r for 110-

125 volt op ration, it is strongly urg d that a conspicuous

lab l or tag b attach d to th pow r cabl to avoid accid ntal

conn ction to 220-250 volt lin s lat r on.

Pow r Cabl Conn ction - Th gr n wir of th amplifi r pow r

cabl is a chassis saf ty ground, and must always (and only) b

conn ct d to th saf ty ground of th a-c mains -- NEVER to on

of th "hot" pow r wir s. Th black and whit wir s ar int r

chang abl and should b conn ct d to th two "hot" conductors

of th s rvic .

4. High Voltag Tap S l ction: If your amplifi r do s not contain

th high voltag tap chang r lay with a front pan l Hl/LO switch,

it was shipp d from th factory with th int rnal HV tap conn ct d

for full pow r SSB op ration. This conn ction is also suitabl

for k y d CW and for int rmitt nt duty FSK or SSTV op ration at up

to on kilowatt d-c input. For continuous or oth rwis h avy-duty

carri r op ration, slightly high r ffici ncy and cool r op ration

may b achi v d by moving th int rnal tap to th m dium voltag

(MV) position, as follows:

(a) DISCONNECT A-C POWER; r mov amplifi r top cov r; short crowbar.

(b) On HV & control circuit board locat d at right, front of th

chassis, not short loop of blu HV wir t rminat d in a f mal

quick-conn ct (QC) lug. For normal high voltag SSB op ration

this blu wir is mat d with anoth r blu HV wir from th main

wiring harn ss ..• via th r ar-most doubl mal QC lug on th

circuit board. To conn ct inst ad th m dium voltag tap, r 

mov only th f mal QC lug conn ct d to th short blu jump r

wir and push it fully on to th front-most mal QC lug (which

is alr ady also conn ct d to a gr n HV wir from th harn ss).

No-load plat voltag will th r by b r duc d from 2.4 KV (HI)

to approximat ly 1.6 KV (LO).

It is d sirabl that you familiariz yours lf with amplifi r op ra

tion, and p rform initial tun -up, using th "L O ” tap. A chart of

TUNE and LOAD control s ttings d t rmin d und r th s conditions

will th n p rmit pr s tting th controls v ry clos ly wh n changing

fr qu ncy th r aft r, r quiring only minor touch-up in op ration.

NOTE* Us of th optional HV tap chang r lay p rmits conv ni nt

(and on-th -air l gal) tun -up at on kilowatt input; switching

th n to th HI position pr par s th amplifi r instantly for full

pow r SSB op ration at 2+ KW. PEP input -- without furth r adjustm nt.

5* Physical Locationt Th ALPHA 76 must b locat d so that intak of

cool air through th r ar pan l, and xhaust of hot air through

th top cov r p rforations, is not imp d d in any way. A minimum

of 4 to 6 inch s of cl aranc should b allow d b hind and abov

th amplifi r cabin t for air circulation. B car ful not to

block th top-cov r xhaust op nings with log books or quipm nt.

6. RF And Control Conn ctions : Int rconn ction of th ALPHA 76 for

op ration with any popular transc iv r or xcit r is xtr m ly

simpl . Conn ct th r ar pan l jacks as follows:

RF INPUT - Us a standard "RCA" typ plug and RG-58C/U or similar

small 50 ohm coaxial cabl to conn ct to transc iv r or xcit r

"rf output” or ’’ant nna" conn ctor. K p cabl short if possibl .

RF OUTPUT - Us a standard PL-259 ("UHF" typ ) plug and RG-8A/U

or similar 50 ohm coaxial cabl to conn ct to ant nna syst m.

RELAY - Us a standard "phono-typ " patch cabl to conn ct this

jack to contacts which ar "op n" on r c iv and "short d" on

transmit ("N.O." -- normally op n). Such contacts ar usually

availabl on th r ar pan l of th xcit r or transc iv r in th

form of a matching "phono" conn ctor. A f w transc iv rs, such

as Atlas and Drak uni*t^ may r quir sp cial conn ctors for

tying into th ir int rnal transmit-r c iv r lay contacts.

NOTE: Wh n th amplifi r is OFF or in th RECEIVE condition with

no short across th RELAY lin , th RF OUTPUT conn ctor is int rnally

conn ct d dir ctly to th RF INPUT conn ctor, providing normal

"transc iv -typ " ant nna input to th r c iv r.

ALC - For us with conv ntional transc iv rs having n gativ -

going ALC syst ms, simply patch this jack to th mating ALC jack

on th transc iv r (or xcit r), using standard "phono” cabl .

C rtain solid-stat transc iv rs utiliz positiv -going ALC which

r quir s slight modification of th amplifi r's ALC circuit, or

us of an adapt r, if ALC f dback is to b mploy d. Normally

it is quit satisfactory to simply us th transc iv r's int rnal

ALC syst m with Atlas, Triton, and similar radios.

-5-

1. Control Functions:

BAND - S l cts tuning rang of amplifi r, indicating th nominal

c nt r of th rang in MHz.

TUNE - Controls amplifi r r sonant fr qu ncy. In g n ral, high r

fr qu ncy bands (28 & 21 MHz, tc.) tun n ar r to th ”0"

nd of th v rni r dial scal , whil low r-fr qu ncy bands

(3*5 and 1.8 MHz) tun mor in th 50 to 100 rang .

LOAD - Controls d gr of amplifi r loading. High r bands (28 &

21 MHz) load prop rly toward th 70-100 nd of th v rni r

dial scal , low r bands mor in th 0-50 rang . In g n ral,

adjusting toward a high r numb r r sults in a h avi r load

ing of th amplifi r.

ON/OFF - Controls main a-c pow r to amplifi r. Also s rv s as

"r s t" control aft r pow r turn-off by ov rcurr nt r lay.

Hl/LO - (Optional on PA-76 and PA-76P, standard on PA-76C) S l cts

"high" or "m dium" HV tap for SSB or CW/TUNE/FSK/SSTV op ra

tion, r sp ctiv ly.

PUSH BUTTONS -

STBY: Disabl s amplifi r chang ov r r lay, th r by p rmit

ting "straight-through" op ration of xcit r/trans

c iv r whil amplifi r r mains r ady for us . M t r

monitors amplifi r high voltag (HV: 3 KV full scal ).

OPERATE-HV (2nd button): P rmits normal op ration of ampli

fi r whil m t r monitors HV.

GRID: Normal op ration, m t r monitors grid curr nt (150

milliamp r s full scal ).

PLATE: Normal op ration, m t r monitors plat curr nt

(1.5 amp r s full scal ).

FWD: Normal op ration, m t r monitors rf forward pow r

(2000 watts full scal ).

REFL: Normal op ration, m t r monitors rf r fl ct d pow r

(200 watts full scal ) for d t rmining load VSWR.

ALC (r ar pan l adjustm nt) - S ts driv pow r l v l at which

ALC voltag b gins to ris from z ro; s ts "ALC thr shold."

2. Tun -Up Proc dur :

(a) GENERAL - Th nd goal of tun -up is to adjust th amplifi r

for maximum pow r output at th int nd d/d sir d l v l of

driv pow r and d-c plat input. If a st ady carri r at a

fix d pow r l v l is appli d to th RF INPUT and th ALPHA 76

TUNE and LOAD controls ar prop rly adjust d to yi ld th

maximum availabl rf pow r output, th amplifi r is automatic

ally s t up prop rly for th b st combination of ffici ncy

and lin arity possibl at that driv l v l.

SECTION 3

OPERATION

-6-

If th driv pow r is incr as d b yond th tun -up l v l

aft r th final TUNE/LOAD adjustm nts, flattopping and un

d sirabl distortion (on SSB) will r sult, along with grid

curr nt gr atly in xc ss of normal.

If driv pow r is r duc d b low th tun -up l v l without fur

th r adjustm nt of TUNE and LOAD controls, amplifi r ffici ncy

will b r duc d. Both of th s stat m nts ar applicabl to

any lin ar amplifi r of th typ s us d for high pow r amat ur

and similar s rvic .

It is th r for ss ntial that th amplifi r b adjust d for

maximum rf output at th driv and d-c input pow rs which ar

to b mploy d in normal op ration, WITH ONE IMPORTANT EXCEPTION:

if th plat voltag is chang d without changing also th TUNE

and LOAD adjustm nts, th r sulting pow r l v l which will yi ld

optimum p rformanc at th n w plat voltag will vary in pro

portion to th squar of th plat voltag chang . For xampl ,

if th ALPHA 76 is tun d up for maximum output with 1400 VDC

plat voltag and with th driv l v l s t so that th r sult

ant maximum output is about 700 watts ( quival nt to a d-c

input of roughly 1000 watts), THEN if th plat voltag is

incr as d to 2000 VDC th amplifi r will automatically p rform

optimally at about 700 X (2000/1400)2 = 1400 watts rf output,

corr sponding to approximat ly 2000 watts d-c input.

In g n ral, th final op rating adjustm nt aft r basic tun -

up should b to adjust xcitation (driv ) from th xcit r or

transc iv r so that th GRID curr nt m t r indication just

r ach s about 50 mad (l/3 scal ) k y-down or on voic p aks.

(b) INITIAL TUNE-UP - S l ct m dium plat voltag by ith r placing

th pan l switch controlling th (optional) HV tap chang r lay

into its L0 (down) position or s l cting th int rnal MV tap

b for installing th amplifi r cov r during installation.. Mak

c rtain that th top cov r is prop rly fast n d in plac .

(1) Pr ss STBY button and mom ntarily lift th ON toggl .

Th pan l m t r should imm diat ly illuminat r d or

amb r and indicat 1,5 KV (mid-scal ) + 100 V. Th

blow r should start imm diat ly and xhaust air should

b r adily d t ctabl flowing from th top cov r v nts.

(2) Wh n th tub warm-up d lay is compl t d in 45 to 90

s conds, th m t r will chang from amb r to pal gr n,

indicating ’’r ady" to transmit. S t controls to th pr 

liminary points indicat d in Tabl I b low, d p nding

on th d sir d op rating fr qu ncy.

TABLE I -- PRELIMINARY SETTINGS FOR INITIAL TUNE-UP

FREQ.. MHZ

1.8 BAND TUNE LOAD FREQ. BAND TUNE LOAD

1.8 84 30 7.1 7 50 45

2.0 1.8 75 25 14.15 14 21 70

3.6 3.5 53 38 21.20 21 10 82

3.9 3.5 42 48 28.70 28 08 85

(3) Pr ss PLATE button and switch xcit r to CW or TUNE;

th pan l m t r should turn amb r to indicat 'transmit.'

(4) V ry slowly incr as xcit r carri r output until th

amplifi r pan l m t r indicat s plat curr nt of 0.5

amps (1/3 scal ). Pr ss FWD button and car fully ad

just LOAD control for maximum m t r indication. Th n

adjust TUNE for maximum m t r r ading, and r p at th

proc ss of alt rnat ly adjusting first LOAD, th n TUNE,

until no furth r incr as in FWD pow r is obtainabl .

(5) Pr ss PLATE button and not m t r indication; th d sir d

r ading for on kilowatt d-c input is approximat ly 0.7

amp (sinc 0.7 amp X 1400 volts = 980 watts input).

(6) If th plat curr nt in st p (5) was l ss than 0.7 amp,

incr as xcit r carri r output slightly and r p at th

LOAD/TUNE adjustm nt proc ss of st ps (4) and (5) again.

If th plat curr nt in st p (5) is gr at r than 0.7 amp,

d cr as xcit r output slightly and r p at th LOAD/TUNE

proc ss of st ps (4) and (5) again.

(7) Continu making slight corr ctions in driv pow r, and

th n .adjusting LOAD and TUNE alt rnat ly for maximum

FWD pow r output until, aft r th final adjustm nt, th

PLATE curr nt m t r indication is v ry clos to 0,7 amp.

(8) Th ALPHA 76 is now corr ctly adjust d for op ration at

on kilowatt d-c input using th m dium plat voltag

tap.

in (b) just abov . L av amplifi r in m dium ('LO*) plat

voltag condition. Ch ck xcit r rf output (mik gain,

cw l v l, or rf output control, as applicabl ) to insur

that k y-down amplifi r GRID curr nt r ading is about

50-75 ma (1/3 to l/2 scal ). On SSB s t mik gain or

xcit r rf output l v l so that GRID curr nt r ading on

sp ch p aks do s not xc d 40-50 ma (l ss than 1/3 scal ).

(d) OPERATION ON SSB AT 2+ KW PEP INPUT - Tun up xactly as

in (b) abov . R mov xcitation. Switch (optional) HV

tap-chang r lay to 'HI* position if availabl ; oth rwis

r mov all pow r from amplifi r, op n top cov r, and chang

ov r to high voltag tap position as d scrib d on pag 3i

paragraph 4 (blu -to-blu wir s). R plac cov r, r conn ct

a-c pow r, and switch ALPHA 76 ON,

Wh n m t r lights gr n, switch xcit r to SSB and sp ak

normally into th mik whil adjusting mik gain (or rf

output) control so that high st m t r swings with th PLATE

button d pr ss d r ach approximat ly 0.45 amp (just und r

l/3 of full scal ), OR until high st GRID curr nt swings

r ach 50 ma (1/3 scal ), which v r occurs first.

Maximum (U.S.) amat ur pow r input of on kilowatt av rag

corr sponds to high st PLATE m t r swings of about 0.45

amp, as d scrib d abov , provid d that plat voltag (HV)

drops to approximat ly 2.2 KV on sp ch p aks. D p nding

on individual voic and xcit r charact ristics, it may

b d sirabl to initially adjust for loading slightly

light r (or h avi r) than d scrib d abov so that SSB

sp ch p aks of 0.45 amps PLATE and 30-5° ma GRID curr nt

occur simultan ously.

( ) TUNE-UP UNDER "HV" CONDITIONS - Wh n th optional HV tap

chang r lay is not includ d, th ALPHA 76 may saf ly "b

tun d-up with maximum plat voltag appli d so that th in

t rnal taps n d not b chang d. Extra car must b x rcis d,

to avoid abusing th amplifi r or tub s, to insur that (a)

driv pow r is k pt low and adjust d v ry car fully, with LOAD

adjust d first and TUNE s cond at ach st p and that (b) PLATE

curr nt is not p rmitt d to xc d 0.7 amp for long r than 15-

20 s conds at a tim , nor 1.0 amp at any tim .

(1) For On Kilowatt Input With HI Plat Voltag , follow th

sam basic proc dur as d scrib d in st ps (4) through

(7) xc pt mak all adjustm nts for a final "targ t"

PLATE curr nt of approximat ly 0.45 amp (X approx. 2.2 KV =

1000 watts input). (R f r nc : pag 7*)

(2) For 2+ KW PEP SSB Op ration, tim up in HV just as in st ps

(4) through (7) on pag 7 for L0 voltag tun -up xc pt

th final plat curr nt goal is 1.0 amp at th nd of th

last LOAD/TUNE adjustm nt it ration. (NOT LEGAL ON ANTENNA!)

ALWAYS ADJUST LOAD CONTROL FIRST, THEN TUNE! Vary th

xcitation in small st ps, as n c ssary, until th d sir d

plat curr nt is achi v d at maximum output. Th n switch

xcit r/transc iv r to SSB and adjust mik gain as d scrib d

on pag 7«

NOTE! Wh n op rating at on kilowatt carri r or PEP input in

th HI plat voltag condition, th maximum driv pow r

r quir d is only about 50 watts, typically. S v r

ov rdriv may r sult in s rious damag to tub s or rf

tuning circuits which may not b cov r d by warranty.

3* ALPHA 76P and ALPHA 76C Op rating Diff r nc s:

(a) Plat curr nt valu s r f rr d to in pr vious pag s in conn ction

with tun -up and op ration of th ALPHA 76 may g n rally b

incr as d by 40-50# for th thr tub "P" and "C" mod ls;

corr sponding grid curr nts will typically incr as 40-50$ as

w ll. This allows both th 76P and th 76C to op rat at

40-50$ high r l v ls of p ak or int rmitt nt pow r input and

output.

(b) Th xtra-duty 2.4 KVA Hip rsi3®pow r transform r us d in

mod l ALPHA 76C p rmits this mod l to op rat at a long-t rm

av rag or continuous pow r l v l approximat ly 50-60$ gr at r

than that of th ALPHA 76 or 76P — about 1.5-1«6 KW d-c input

and 1 KW rf output, continuous duty, v rsus 1.0 KW d-c input

maximum (continuous or av rag ) for th 76 and 76P.

against accid ntally xc ding th long-t rm/CCS av rag d-c

input rating of 1 KW. This normally is not a probl m xc pt

possibly in th v nt of continuous k y-down op ration or

continuous SSB transmission with h avy sp ch proc ssing.

20 amp 3AB or ABC fus s may b substitut d for 120V op ration.