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G8MNY > TECH 24.12.12 16:33l 269 Lines 13816 Bytes #999 (0) @ WW
BID : 5743_GB7CIP
Read: DK3UZ GUEST
Subj: T500M 12V 500W HF Linear
Path: DB0FHN<DB0MAK<DB0ERF<IZ3LSV<I0OJJ<UA6ADV<GB7CIP
Sent: 121224/1415Z @:GB7CIP.#32.GBR.EU #:5743 [Caterham Surrey GBR] $:5743_GB7C
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Dec 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I bought this old (1977) large commercial Trans World Electronics Inc, 12V HF
Amp for "MEDIUM POWER Air/Ship" use. at a local junk sale. It was quite cheap &
came with handbook, so I expected some problems.
/////////////////////// 2-30MHz, 4x 150W push pull amps
///////////////////////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
/////////////////////// / ³ 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 (SWR & over Drive)
³ o<ð [__] [____] ³/ Manual & Remote operation (On & Band select)
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ Weight 8kg.
It basically worked OK "no blown amps".
SCHEMATIC
Rx Through Path
DriveÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
Rig__/ ÚÄÄÄÄÄ¿50êÚÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄ¿50ê ÚÄÄÄÄÄÄ¿ \__Ant
|ÀÄÄÄ´AttenÃÄÄÄ´Splitter³ ³CombinerÃÄÄÄÄÂÄ/Ä´FilterÃÄ\ÄÂÙ
| 70WÀÄÄÄÄÄÙ50WÀÄÂÄÂÄÂÄÂÙ 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> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
But there was a fault, a "light contact" on the single wafer band control
switch, causing non operation or no band filter selection (no RF output path!)
That was easily fixed once it was stripped down.
LAYOUT (Bottom cover off)
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ ³
Þ³~~~~~ÄÄ Pot PushPull³ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÃÄ¿
ݳ100 ³ Bias () ²²²²Output ³Relay³ >15MHz Filter ³Relay³ ÃÄÙ
ݳAmp ³ Circuit [ð] PA1 Transformers ~~~~~ ~~~~~ ³Rig
Þ³Meter³ [ð] () ²²²² ³ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ³
³-----~~ [ð]Input ³Relay³8-15MHz Filter ³Relay³ ³ÜÛ
³ [ð]Spliter () ²²²² ³ ~~~~~ ~~~~~ /³+ß 13.6V
³ÄÄÄÄÄÄ. [ð] [ð] PA2 ÚÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄĿݳ-Ü DC
³75A DC ÃÄÄ[ð] [ð] () ²²²² ³ DC ³ ³Relay³ 5-8MHz Filter ³Relay³Û³ßÛ
Þ³TRIP & Ã()shuntÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜRelay³ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÛ³
/³ON/OFF ³__Üßßßß () ²²²² ÀÄÄÄÄÙ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ³12 Way
ß³======' PushPull[ð] PA3 ³ ³Relay³ 3-5MHz Filter ³Relay³ ³Jones
³Drive³ Drive[ð] () ²²²² [ð]Output~~~~ ~~~~~ ³Socket
³Relay³ Transformers [ð]CombinerÄÄ¿ ÚÄÄÄÄÄ¿ ³
³~~~~~ () ²²²² [ð] ³ ³Relay³ 2-3MHz Filter ³Relay³ ³
³| ThermSw [ð] PA4 [ð] ~~~~~ _____ ³Ant
[³|Band [ð] () ²²²² ³ ³ Ant ³ ÃÄ¿
³|Switch :RF lead: ³Relay³ ÃÄÙ
³ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~~~~ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
The 75A fast magnetic trip has an external calibrated shunt & the 100A ammeter
uses 10cm of the thick lead as its calibrated shunt.
A simple 2 transistor thermally tracked circuit provides the 2.2A of current
limited bias @ 0.69V for the 4 class AB push pull amps. Excluding bias current
through 5R, total PA quiescent current should be 1.6-2A.
The 4 identical push pull Amps use 8x PT9847 100W HF transistors & the inputs &
outputs are wired up from the splitter & to the combiner with staggered lead
lengths, so all the RF signals ends up exactly in phase. The splitter &
combiner both have out of balance dump resistors to soak up amplifier
differences for best stability & linearity.
There are 10 relays that switch in one of the selected five 2 section PI filter
2-3, 3-5, 5-8, 8-15, & 15-30MHz, to reduce the PA harmonics to -43dB.
N.B. there no PA output path without both of these relays operated OK!
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.
MY MODIFICATIONS
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 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 2N ÃÄððÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄ<PTT
³ 3703 /³ Fbead 80mA
_³_ _³_
/// /// Back EMF diodes & RF caps not shown
2/ FILTER RELAY CURRENT
Also the input & output Tx filter relays (not in Rx path) are now only operated
when the PTT is active from a PNP emitter follower. Being the last to operate,
the drive relay is also buffered. But the Ant relay must be faster, so it is
left directly on the PTT line! About 300mA is saved on standby with these
modifications. It also reduces the PTT current (limited PTT current reed relay
on my exciter).
3/ RIPPLE SMOOTHIMG
The amp only had 3x 1000uF on the PA 12V, the diagram showed 3x 2200uF, &
having a large bag of similar 1000uF caps, I added 7 more symmetrically stacked
up around the 4 amps to give 10,000uF in all. These can give a few amps each at
AF reducing the battery lead ripple current.
4/ DC LOSSES
On this QRO amp with these very high currents a drop of 1V = 100W less peak
power! DC losses on leads & unsoldered crimp connectors all adds up. So with
the amp into a dummy load, I use a DVM on 2V range from the battery -ve & +ve
to show up the voltage drops on the leads, contactor, & tags. If RF gets up
your meter use 1k R in series as RF stopper at the probe end.
The metal case connections had not been used to help reduce the internal earth
wire loss, & were 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 cables used are all "starting cables" with soldered on drilled copper
ends, & sheathed as much as possible to reduce shorting possibilities!
5/ DC FUSE
There was no low current fuse, so I added a 3A one in the small wiring feed to
reduce the risk of internal fire!
6/ 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>ÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄ¿
470 5R ³
³ PA 10W ³
ÀÄÄ>Bias<ÄÄÄÄÄ´ 15K
Circuit 270 ³
³ ³
PNP 2N e\³ 10K 50W-
3703 on ÃÄÄÄ>POWER 600W
POT /³ POT Adjustment
ÚÄÄÄ´ _³_
4K7 |³| ///
70W 1N4148 ³ ³Fbead
AMP RF >Ä1kÄ´<ÃÄ´<ÃÄ´ ³ 1N4148 u1 0V to -10V
Drive ³ ÀÄÄÄÄÄÄÄÄÄÄððij<ÃÄÄÂÄÄÄÂÄÄÄ>ALC to rig
Atten n22=== Fbead 4K7 === on spare
_³_ _³_ _³_ Jones pin
/// /// ///
The -ve supply for the ALC is derived from the drive RF. It is clamped +ve by
the PNP when the PA bias current (up to 2.2A) through 10W 5R (proportional to
RF DRIVE) gives a voltage higher than that set on the POWER POT. This gives
exciter drive power reduction as the PA 12V drops keeping PA spectrum clean.
7/ INPUT SWR
The input frequency compensating attenuator circuit was not as the diagram &
the SWR was not that good. All components tested 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())ÄÂÄÄÄÄÂÄÄÄÂÄÄÄÄÂÄ´ÃÄÄÂÄ>Drive
L2( === ÃÄ220Ä´ Splitter ³ L2( === ÃÄ200Ä´ Splitter
( ³56p ÃÄ220Ä´ === ( ³56p ÃÄ200Ä´
ÚÄÄÄÂÁÄÄÂÁÄÄ¿ ÀÄ220Ä´ 60p³ ÃÄÄÄ´ ÃÄ200Ä´
200 200 200 200 220 ³ 220 220 ÀÄ200ÄÙ
_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
disconnect 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 jucntion. I found making this
a 60pF (Tx grade) was better at 10m & changing the load Rs around gave a better
lower band input match.
Flat gain is less important than driver rig linearity, due to poor input load.
The input SWR will change with drive level (higher Z at more power), as the RF
NFB level reduces correcting the amp gain as each amp works harder.
TESTING
At a club meeting 2 of these amps (modified & unmodified) were tested with 2
tone linearity test & with a spectrum analyser for harmonics. Both amps
performed well to the 600W at 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 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.
HAZARDS
Current Loops
Although 12V is fairly safe, with high currents anything metal is a hazard!
This includes the rig's PL259 plug & mains earth wiring! Care must be take to
ensure the 75A does not flow around unsuitable leads in parallel!
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!
Anti Explosion Tip
Always "blow at the battery" before making/unmaking connections, this reduces
the chance of hydrogen being around for sparks to ignite!
High Power RF
At these powers RF leakage from loose PL259s & 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!
Wind coax or balanced aerial leads to make "RF chokes" near shack end, to get
the shack RF fields & lead currents down!
See my Tech bul "AF 2 Tone Test Osc Design", "Transistor PA Biasing",
"Lead Acid Batteries", "2nd Car Battery for /M & /P", &
"Rig DC Power & RF Hazards"
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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