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G8MNY > TECH 09.10.14 09:28l 348 Lines 17651 Bytes #999 (0) @ WW
BID : 12099_GB7CIP
Read: GUEST
Subj: T500 M 12V 500W HF Linear
Path: IW8PGT<IZ3LSV<IV3SCP<IW0QNL<JH4XSY<JE7YGF<7M3TJZ<CX2SA<GB7CIP
Sent: 141009/0628Z @:GB7CIP.#32.GBR.EURO #:12099 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 14)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I bought an old (1977) large commercial Trans World Electronics Inc, 12V HF Amp
for "MEDIUM POWER Air/Ship/Army" use. at a local junk sale.
///////////////////////³ 2-30MHz, 4x 150W push pull amps in parallel.
/////////////////////// ³ > 10dB gain, 70W max drive.
/////////////////////// /³ IMD 3rd Order -32dB @-500W, -36dB @ 400W.
/////////////////////// / ³ PA harmonics to -43dB.
/////////////////////// / ³ 13.6V @ 75 Amps needed for full 600W output!
/////////////////////// / / 1kW DC input, Infinite SWR rated, <2:1 recom.
³³³³³³³³³³³³³³³³³³³³³³³³ / / 15A charger & car battery will power it (SSB).
ÚÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ¿ / Thermal 70øC heatsink shutdown.
³T500M __ ____ ³ / Over current 75A trip (high SWR & over drive).
³ o<ð [__] [____] ³/ Manual & Remote operation (On & Band select).
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ Weight 8kg.
It was quite cheap & it came with the handbook, so I expected some problems. On
examination it basically worked OK "no blown amps", but a faulty band switch.
That was just a "light contact" on the single wafer switch, causing non
operation, or no "band filter relays" selected (no RF output path!) & easily
fixed once the switch was stripped down.
S C H E M A T I C
Rx & low power through path
DriveÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
Rig__/ ÚÄÄÄÄÄ¿50êÚÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄ¿50ê ÚÄÄÄÄÄÄ¿ \__Ant
|ÀÄÄÄ´AttenÃÄÄÄ´Splitter³ ³CombinerÃÄÄÄÄÂÄ/Ä´FilterÃÄ\ÄÂÙ
| 70WÀÄÄÄÄÄÙ30WÀÄÂÄÂÄÂÄÂÙ ÚÄÄÄ¿ ÀÂÄÂÄÂÄÂÄÙ600W³ | ÀÄÄÄÄÄÄÙ | ³
| Max ³ ³ ³ ÀÄÄ´PA1ÃÄÄÙ ³ ³ ³ ³ ÚÄÄÄÄÄÄ¿ ³
| ³ ³ ³200êÀÄÄÄÙ200ê³ ³ ³ ÃÄ/Ä´FilterÃÄ\Ä´
| ³ ³ ³ ÚÄÄÄ¿ ³ ³ ³ ³ | ÀÄÄÄÄÄÄÙ | ³
PTT>ÄÙ Drive ÚÄÄÄÄ¿ ³ ³ ÀÄÄÄÄ´PA2ÃÄÄÄÄÙ ³ ³ ³ ÚÄÄÄÄÄÄ¿ ³
/Ä´BiasÃ> ³ ³ 200êÀÄÄÄÙ200ê ³ ³ ÃÄ/Ä´FilterÃÄ\Ä´
³ ÀÄÄÄÄÙ ³ ³ ÚÄÄÄ¿ ³ ³ ³ | ÀÄÄÄÄÄÄÙ | ³
Trip ³ ³ ÀÄÄÄÄÄÄ´PA3ÃÄÄÄÄÄÄÙ ³ ³ ÚÄÄÄÄÄÄ¿ ³
ÚÄÄ¿ ³ ³ 200êÀÄÄÄÙ200ê ³ ÃÄ/Ä´FilterÃÄ\Ä´
DC_³/_³_/ÄÁÄ> ³ ÚÄÄÄ¿ ³ ³ | ÀÄÄÄÄÄÄÙ | ³
ÀÄÄÙ |DC ÀÄÄÄÄÄÄÄÄ´PA4ÃÄÄÄÄÄÄÄÄÙ ³ ÚÄÄÄÄÄÄ¿ ³
| 200êÀÄÄÄÙ200ê ÀÄ/Ä´FilterÃÄ\ÄÙ
Band Switch | ÀÄÄÄÄÄÄÙ |
or Remote> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
L A Y O U T (Bottom cover off)
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ Äij
Þ³~~~~~ÄÄ Pot PushPull³ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÃÄ¿
ݳ100 ³Bias () ²²²²Output ³Relay³ >15MHz Filter³Relay³ ÃÄÙRig
ݳAmp ³Circuit [ð] PA1 Transformers ~~~~~ ~~~~~ ³SO239
Þ³Meter³ [ð] () ²²²² ³ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ³
³-----~~5R [ð]Input ³Relay³8-15MHz Filter³Relay³ ³ÜÛ 13.6V
³ [ð]Spliter () ²²²² ³ ~~~~~ ~~~~~ /³+ß DC 75A
³ÄÄÄÄÄÄ. [ð] [ð] PA2 ÚÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄĿݳ-Ü Wing
³75A DC ÃÄÄ[ð] [ð] () ²²²² ³ DC ³ ³Relay³ 5-8MHz Filter³Relay³Û³ßÛ Nuts
Þ³TRIP & Ã()shuntÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜRelay³ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÛ³
/³ON/OFF ³__Üßßßß () ²²²² ÀÄÄÄÄÙ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ³12 Way
ß³======' PushPull[ð] PA3 ³ ³Relay³ 3-5MHz Filter³Relay³ ³Jones
³Drive³ Drive[ð] () ²²²² [ð]Output~~~~ ~~~~~ ³Socket
³Relay³ Transformers [ð]CombinerÄÄ¿ ÚÄÄÄÄÄ¿ ³
³~~~~~ () ²²²² [ð] ³ ³Relay³ 2-3MHz Filter³Relay³ ³
³| ThermSw [ð] PA4 [ð] ~~~~~ _____ ³SO239
Û³|Band [ð] () ²²²² ³ ³ Ant ³ ÃÄ¿Ant
³|Switch :RF lead: ³Relay³ ÃÄÙ
³ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ~~Äij
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
The 75A fast magnetic trip has an external calibrated shunt, the 100A ammeter
uses 10cm of the thick DC lead as it's calibrated shunt.
Bias is a simple 2 transistor thermally tracked circuit provides up to 2.2A of
current @ 0.69V for the 4 class AB push pull amps. Excluding bias current
through the 5R, total PA quiescent current should be 1.6-2A, & it does give the
best two tone results at around that level. See 6/
P A R A L L E L A M P S
The 4 identical push pull Amps use pairs of PT9847 100W HF transistors, the
inputs & outputs are wired up from the drive splitter & to the output combiner
with staggered lead lengths, so all the RF signals ends up exactly in phase.
ÚÄÄÄÄÄÄ>PA1>ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
(|_100_ _100_|)
_(| ³ 200ê ³ |)_
³ (|_100_³ AMPS ³_100_|) ³
³ (| ³ ³ |) ³
³ ÀÄÄÄÄÄÄ)ÄÄÄ>PA2>ÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÙ ³
50ê ³ ³ ³ ³ 50ê
Drive>Ä´SPLITTER³ ³COMBINERÃÄ>Output
30W ³ ³ ³ ³ 600W
³ ÚÄÄÄÄÄÄ)ÄÄÄÄÄÄÄ>PA3>ÄÄÄ)ÄÄÄÄÄÄ¿ ³
³ (|_100_³ ³_100_|) ³
³_(| ³ 200ê ³ |)_³
(|_100_³ AMPS ³_100_|)
(| |)
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ>PA4>ÄÄÄÄÄÄÙ
The splitter & combiner both have out of balance dump 100R resistors of 1W & 5W
to soak up any amplifier differences for best stability & linearity.
There are 10 relays that switch the selected QRO five 2 section PI filters 2-3,
3-5, 5-8, 8-15, & 15-30MHz, to reduce the PA harmonics to -43dB. N.B. there is
no PA RF output path without a band pair of relays operated!
At 25øC ambient in free air, the very large heatsink does not need a fan on 50%
duty SSB, despite only the front part getting hot. But carrier modes are to be
avoided (input attenuator overheats on lower bands!) or the temperature might
rise above the thermal 70øC auto resetting cut off switch.
M O D I F I C A T I O N S
1/ LED INDICATORS & STANDBY RELAY CURRENT
Current was quite high in Rx mode, I found all the relays would operate OK
down to 7V. So I added series Rs to reduce the currents 30% for the slow to
operate ones, & used the added R voltage drop to light 2 status LEDs.
ÚAmmeter¿ Op Drive
+12V>ÄTRIPÁÄShuntÄÁÂÄÄÄÄÄ\ÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄ\ÄÄ>Bias
75A ÚÄÄÄÄÁÄÄÄÄ¿ ÚÄÄÁÄÄÄ¿ === PA ÚÄÄÁÄÄ¿ÚÄÄÁÄÄ¿ Regulator
³ DC Op ³ ³Filter³ _³_3000uF ³Drive³³ Ant ³
³Contactor³ ³Relays³ /// ³Relay³³Relay³
ÀÄÄÄÄÂÄÄÄÄÙ ÀÄÂÂÂÂÂÙ ÀÄÄÂÄÄÙÀÄÄÂÄÄÙ
ÚÄ100Ä´ ³³³³³ Red ÚÄ100Ä´ ³
Green _³_ 1W oooooo Tx _³_ ³ ³
ON <=\_/ 75R /³\ LED<=\_/ 33R ³
LED ÀÄÄÄÂÂÅ¿ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÙ ³
oooooo e\³ ³
/³\ PNP ÃÄððÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄ<PTT
³ 2N2905/³ Fbead 80mA
_³_ _³_
/// /// Relay back EMF diodes & RF caps not shown
Added components mounted on or near the band switch.
2/ FILTER RELAY CURRENT
Input & output filter relays (not in Rx path) are now only operated when the
PTT is active from a PNP emitter follower. The drive relay being last to
operate is also buffered. But the Ant relay must be faster, so it is left
directly on the PTT line! These modification save about 300mA on standby. It
also reduces the PTT current to 80mA (limited PTT current on my exciter's reed
relay).
3/ RIPPLE SMOOTHIMG
Only 3x 1000uF was fitted on my PA, the diagram showed 3x 2200uF, & having a
large bag of similar 1000uF caps, I added 7 more symmetrically stacked up
around the 4 amplifiers to give 10,000uF in all. Each of these can give a few
amps at audio, reducing some of the battery lead ripple current.
4/ DC LOSSES
This QRO amplifier has very high currents, a drop of 1V = 100W less peak
power! DC losses on leads & unsoldered crimp connectors all adds up. So with
amplifier into a dummy load, I use a DVM on 2V range from battery -ve & +ve to
show up where the voltage was being lost... drops on the leads, contactor, &
tags. (If RF gets up your meter use 1k R in series as RF stopper at probe end)
Metal case connection had not been used to help reduce the internal earth
wire loss, & it was just bolted on painted panels. So I ground off the paint
around the earth post, greased the bare aluminium to keep the air away, &
bolted it up tightly. I did the same to rear panel to heatsink screws with
lock washers etc.
External DC cables, I use "starting grade cables" see "battery leads" below,
5/ DC FUSE
There was no low current fuse, so I soldered in a 3A one in the small wiring
feed to reduce the risk of an internal fire!
6/ BIAS
I found this circuit slightly unstable (when scoping the R5 5R), but a small
capacitor base to collector, on the large NPN stopped it. Components were not
the same as original diagram!
PTT Switched
+12V ÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ R5
R4 Added 5R
270 47n 10W
³ Ú´Ã---³ <--Scope for 1MHz oscillation
³ | ³/c
ÃÄÄÄÄÄÂÄÄÄÄÄ´ TIP33A
³ C6 === Q2 ³\e NPN +690mV
³ 2u2_³_ ÃÄÄÄÄÂÄÄÄÂÄ> via RFC
³ /// ³ ³ ³ to Amplifer
NPN c\³ ³ ³ ³ Input
TIP29 ÃÄÄÄÄÄÄÄÄÄÄÄ´ ³ ³ Transformers
e/³ Q1 _³_ +³ 2R2
PA BIAS ³ \_/ === ³
QuescentÀ>5R D2 ³ C7³ ³
Set 1-2A R3 ³ 2u2³ ³
ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄ
7/ ALC
There is no ALC system on this AMP, & I am used to old Valve amp with a power
ALC control. With PA ALC, the driver power is automatically set to the wanted
level, & with the PA turned off your back to full bare foot power. So I
designed this ALC circuit for this PA.
+12V Tx>ÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
R4 5R ³
270 PA 10W ³
ÀÄ>Bias<ÄÁÄ270Ä¿ 15K
Circuit ³ 2n2 ³
ÃÄĴÿ ³ Front panel
PNP e\³ ³ 10K 50W-600W
2N3703 ÃÄÄÁÄ>POWER ALC Control
on POT /³ POT
ÚÄÄÄ´ _³_
4K7 |³| ///
³ ³Fbead Mounted on 12 way JONES plug
70W -ve³ ³ 1N4148 0V to -10V
AMP RF >Ä1kÄ´<ÃÄ´<ÃÄ´ ÀÄÄÄÄÄÄÄÄÄÄÄÄððij<ÃÄÂÄÄÄÄÂÄÄÄ>ALC to rig
Drive 1N4148 ³ Fbead ³ 100
Atten === ³ ³ -
2n2 ³ 4K7 === 4u7
_³_ _³_ _³_+ 20V
/// /// ///
The -ve supply for the ALC is derived from the RF after the DRIVE relay. It is
clamped after the 4k7 to +ve by the PNP. This happens when the PA bias current
(limited to 2.2A by 10W 5R) reaching the 8 PA bases, gives a voltage higher
than that set on POWER POT. The series diode & 4K7 load mounted on the Jones
plug ensures only -ve voltages are given to the exciter to reduce power drive.
The 4.7u & 100R give a sensiable ALC action.
8/ INPUT SWR
The input frequency compensating attenuator circuit was not asdagram &
the SWR was not all that good, dispite all components testing out OK.
SWR Original Input Match SWR Improved Input Match @ 50W
1.7´ .ú'ú. 1.7´
1.5´''''''''''' 'ú.. 1.5´
1.3´ ''''úúúúú 1.3´ ..úú. ..úú
1.1´ 1.1´''''''''''''' ''''''''
ÀÂÄÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ ÀÂÄÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ
1.8 3.5 5 7 10 14 18 21 24 28MHz 1.8 3.5 5 7 10 14 18 21 24 28MHz
L1 39p L1 39p
>ÄÄ())ÄÄÄÂÄÄÄÂÄÄÄÄÂÄ´ÃÄÄÂÄ>Drive >Ä())ÄÂÄÄÄÄÄÄÂÄÄÂÄÄÄÄÂÄ´ÃÄÄÂÄ>Drive
L2( === ÃÄ220Ä´ Splitter ³ L2( === ÃÄ200Ä´ Splitter
( ³56p ÃÄ220Ä´ === ( ³56p ÃÄ200Ä´
ÚÄÄÄÂÁÄÄÂÁÄÄ¿ ÀÄ220Ä´ 100p³ ÚÄÄÁÂÄÁÄ¿ ÃÄ200Ä´
200 200 200 200 220 ³ 220 220 220 ÀÄ200ÄÙ
_³_ _³_ _³_ _³_ _³_ _³_ _³_ _³_ _³_
Actual Circuit New Circuit
There was a bump at 10MHz & that is from the drive splitter load. L2 & 56pF
disconnects the added load, as the 39pF bypasses the series attenuator Rs on
the higher frequencies, to flatten the amp gain. The original diagram did not
have 220R to ground, but had 20pF to ground @ the L1/2 junction. I found
making this a 100pF (Tx grade) was better on 10m band & changing the load Rs
around gave a better lower band input match.
Flat gain is less important than driver rig linearity, due to poor load. The
input SWR will change with drive level (higher Z at more power), as the RF NFB
level reduces, correcting each amplifier gain, as each amplifier works harder.
T E S T I N G
At a club meeting 2 of these amplifiers (modified & unmodified) were tested
with 2 tone linearity test & with a spectrum analyser for harmonics. Both amps
performed well to the 600W clipping level. But even brief full carrier testing
on lower bands did provide smoke from the underrated input attenuator!
The 2 tone test showed good linearity to 400W PEP, so I the quoted IMD looks
right.
The harmonics tests on a spectrum analyser showed the need to have right low
pass filter selected, as these un-tuned broadband amps are quite harmonic rich
otherwise!
dB Topbands with dB Topband with
0_³ f1 Filter @ 15-30MHz 0_³ f1 Filter @ 2-3MHz
-10_³ ³ -10_³ ³
-20_³ ³ f3 -20_³ ³
-30_³ ³ f2 ³ -30_³ ³
-40_³ ³ ³ ³ f4 f5 -40_³ ³ f2
-50_³ ³ ³ ³ ³ ³ f6 -50_³ ³ ³
-60_³ ³ ³ ³ ³ ³ ³ f7 -60_³ ³ ³ f3
ÀÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄ ÀÄÄÁÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄ
On Topband the 2-3MHz LPF is not really that good for the 2nd harmonic! Higher
bands fared better with filter performance. Of course no problems at all after
a good ATU.
On actual testing into aerial via a high Q QRO ATU, I found it was possable to
get slight PA parasitic oscillation (of the RF envelope) at very high power.
This was only if the SWR was not perfect, it never did this into dummy load!
But with the final tweak to the input attenuator (as above) it tested OK across
all bands, with ATU tuning over a range of SWRs. So sudden high SWR in a tuner
may indicate Tx "parasitic" as well as aerial "arcing" failure!
H A Z A R D S
Current Loops:
Although 12V is fairly safe (compared to 230V or 3kV), with high currents
anything metal is a hazard! This includes the PL259 plug & mains earth wiring!
I put heat shrink sleeving on 259 plug rig lead near the +12V terminal. Care
must be taken to ensure the "75A" does not flow around unsuitable leads in
parallel eg. Mains PSU earths!
Battery leads:
I use short "starter gauge" cables, with soldered on copper tabs/lugs, made
from thin Copper sheet 0.5mm wound on a 8mm drill 1.5 turns. Then flattern one
end, solder to cable (on cooker).
__________ heat shrink
Drilled ___ _____________
Hole ____/ ³~STARTER CABLE
~~~~ÄÄÄÄÙ~ÄÄÄÄÄÄÄÄÄÄÄÄÄ
~~~~~~~~~~~~
Clean up & apply heat shrink sleeve or tape. Drill hole for PA & battery
connections. Mark up + & - with coloured tape. Apply water repellent grease to
tabs, bolt tread, washers etc.
Lead Acid Batteries:
Other than high current & fire hazard of melted leads, batteries have Sulphuric
Acid that always seems to get out & damage cloths etc, you can replace clothes,
but eyes are something else! Take care!
H2 Anti Explosion Tip:
Always "blow" at the battery, before making/unmaking connections, this simple
action reduces the chance of hydrogen being around for sparks to ignite!
High Power RF:
At these powers RF leakage from loose PL259, high Filter & Aerial voltages are
dangerous! Double checking connectors & everything is SAFE before keying up &
testing is essential. Otherwise you will soon learn about deep RF burns & gain
"Respect for the RF" the hard way!
RF Chokes:
Wind coax or balanced aerial leads to make "RF chokes" near shack end, to help
keep shack RF fields & RF lead currents down!
I N U S E
Running it /P for 8 days at a summer camp on HF pile ups, I did find a 24V fan
(quiet on 12V) was useful to cool the front part of the PA & occasionally my
25A linear PSU floating a battery. The rig & PSU were floated on another
battery. This did allow a much smaller petrol generator (650W 2 stoke) to be
used rather than a 2.3kW 4 stroke & QRO Valve Amp. (That was used for cold
night to keep the tent warm!)
See my Tech buls on "AF 2 Tone Test Osc Design", "Transistor PA Biasing", "Lead
Acid Batteries", "2nd Car Battery for /M & /P", "Rig DC Power & RF Hazards",
"Using 2 HF PAs" & "NORTHERN 650W 2 Stroke Genny".
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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