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ACOM1000 TUBE REPLACEMENT INSTRUCTION
-------------------------------------
This step-by-step instruction is about the tube replacement and
idling currents re-adjustment of ACOM1000 power amplifier. Please
follow all details closely since the work is difficult, with many
details to keep track about, and might be dangerous too. Do not
hesitate to contact your local dealer or nearest ACOM's service for
any advice. Please don't attempt tube replacement by yourself, if you
don't feel comfortable with repairs!
W A R N I N G HIGH VOLTAGE! ==================== =======
The amplifier works with high voltages up to 3000V which is LETHAL!
For your safety pull the amplifier power plug out of the mains wall
outlet and WAIT AT LEAST 30 minutes EACH TIME BEFORE you remove the
cover of the amplifier. Disconnect all cables from the amplifier
(grounding last). Do not touch any part inside before ensuring as
described below that no residual voltages are present!
1. REMOVING THE TOP COVER.
a) First pull the amplifier power plug out of the mains wall outlet.
Wait at least 30 minutes (or more if the amplifier has been just
powered up).
b) Using a Philips-2 screwdriver, unscrew 9 pcs of "eco-fix"
flange-button head screws to release the top cover (2x3 pcs on each
bottom-side edge, and three more on the rear-top edge of the box).
Don't unscrew four screws that hold the grid above the tube. Keep all
screws and washer for the mounting procedure later.
Lift the rear edge of the cover slightly (to 2-3cm) and then pull the
cover backwards, in order to release it from front-panel's chutes.
Remove the top cover. Do not touch the part inside for now!
You will see inside:
- the MAINS PCB that is mounted on an aluminum sub-chassis, just
above the big HV transformer;
- the HV rectifier PCB in front of the MAINS PCB (with four big
diodes, one wire-wound resistor, and one disc ceramic capacitor on
it);
- the HV filter PCB, located just below the HV rectifier (with 8
electrolytic capacitors on it).
c) Before proceeding, please make sure that no residual DANGEROUS
VOLTAGES are present in the amplifier. For this purpose take
approximately 1m of WELL-INSULATED lead (adequate for 3000V). Bare it
to about 1cm at both ends. Tighten one end of the wire under the
GROUND STUD (on the rear panel). Only AFTERWARDS, holding the wire BY
THE INSULATION, at a distance of minimum 10cm (4 Inch), touch with
its second end consecutively all parts on the HV rectifier PCB,
especially:
- the HV output J3;
- the wire-wound resistor R12 on its both sides;
- the four HV diodes on their both sides. With the same wire end, on
the MAINS PCB touch the diode D19 on its both sides (it is located at
the PCB edge, near the powerful transistor that is installed on the
chassis).
2. REMOVING THE SCREEN ABOVE THE RF DECK.
Using a Philips-1 screwdriver, unscrew 15 pcs of countersunk-head
screws to release the aluminum cover above the RF deck. Lift and pull
the cover to remove it.
Repeat step 1(c) about residual voltages, this time touching with the
grounded wire the copper strip of the plate anti-parasitic
suppressors and the tube anode.
Check whether the HV LID crowbar makes a reliable short-circuit
across the HV wiring when the cover is missing.
3. OLD TUBE REMOVAL
W A R N I N G HIGH VOLTAGE! ==================== =======
Prior to continue you must be absolutely sure that there are no
residual voltages in the amplifier - see (1) and (2) above!
Be careful - the tube may be VERY HOT!
Prior to remove the tube, you have to uninstall the 16mm (2/3") wide
copper strip with UHF anti-parasitic suppressor, that is installed
between the tube plate and the big ceramic DC-blocking capacitor
(near the plate choke). Use an 8mm-opening wrench to unscrew a
hexagon-head screw (M5 brass) from one side of the capacitor (where
the connection to the plate choke is made via a soldering lug).
Please hold the capacitor for its ceramic body while unscrewing it,
in order not to let the second screw to loosen. Using a Philips-1
screwdriver, unscrew an M3-screw from the plate capacitive divider
(this is aluminum / Teflon cylinder installed near the tube, on the
tube deck). This way, the entire copper strip, along with the UHF
anti-parasitic suppressor is released and can be easily removed from
the tube.
Unclip the anode spring clip from tube cap, while pressing the tube
to the bottom with a finger. Now unthread the temperature sensor
(which seems like a small transistor), out of the rubber chimney.
Then unthread the chimney out of the anode heat sink, together with
the anti-parasitic suppressor and copper strip (please keep track not
to bend the temperature sensor leads).
At last, pull the tube out of its socket, using force directed to TOP
ONLY, since bending may destroy tube socket.
4. INSTALLING A NEW TUBE
C A U T I O N =============
Examine new tube pins before inserting it in the socket. They must be
straight and not inclined in respect to the ceramic base, otherwise
any bent pin could damage the socket's spring contacts, and thus the
socket and/or the tube may become unusable.
a) Put carefully the new tube ON the socket, without neither pressing
nor inserting the pins. Keep track about the pins orientation. There
is a larger gap between two pins (a pin is vacant) and it must
coincide with the corresponding socket's gap. Be extremely careful
about the tube screen-grid ring, not to bend any of the socket's
spring contacts. If needed, slide the tube carefully up and down
while you align these contacts. After that, count the ring contacts:
there must be 16 of them, closely fitting OUTSIDE the tube
screen-grid ring. This ensures that no spring contact has been
damaged during installation.
b) Align tubes pins so that EACH one would lie precisely in the gap,
and at the width center of the socket's spring contacts. Use very
small rotation movements during this alignment. Do not lift tubes
during this operation in order not to disorder screen grid ring
contacts (otherwise repeat the previous step (a).
c) Using a force of NO MORE THAN 50...60N (about 5...6kg or
12...15Lbs.), in VERTICAL DIRECTION ONLY, push carefully the tube
(holding its plate heat sink) in order to insert the tube in the
socket. If you meet a stronger resistance, do not force anymore and
go back to recheck (a) and (b). The tube must fully seat in the
socket.
C A U T I O N =============
After inserting the tube, please recheck all 16 contacts of the tube
screen ring.
d) Orient the silicon rubber chimney (together with the
anti-parasitic suppressor inside) so that:
- the small hole could be threaded over the temperature sensor later;
- the connections to the capacitive divider and to the ceramic
capacitor could be installed to their old places.
Now thread, by small steps in parallel, the chimney over the tube
plate heat sink. Keep track not to bend the temperature sensor during
this operation. Clip the anti-parasitic-suppressor spring contact to
the tube plate and precisely orient the connection lugs to the
capacitive divider nut and to the big ceramic capacitor. Align
carefully the rubber chimney, so that it firmly contact the tube deck
at the base (otherwise a part of airflow would be exhausted uselessly
and the tube might over-heat). At last, install and tighten the
screws to the capacitive divider and the ceramic capacitor, using
their original screws and lock washers (should have been saved at
previous steps).
e) Insure that after the tube replacement all the wiring is restored
to its former condition.
5. IDLING CURRENT ADJUSTMENT.
After each tube replacement, the BIAS voltage needs to be re-adjusted
in order to align the new tube regime. There is an information screen
"Plate Current" on the LCD, foreseen to monitor the plate current
during this adjustment. The adjustment trimmer-potentiometers is
located on the MAINS PCB.
a) Install the cover above the RF deck (15 countersunk screws). In
two of the nuts on the middle chassis panel, near the HV LID crowbar
and the cover-presence micro-switch sensor, tighten two small strip
pieces in order to imitate top cover. Check that they are pressing
the crowbar reliably in order not to let it escape during next
operations.
W A R N I N G HIGH VOLTAGE! ==================== =======
Be careful - HIGH VOLTAGES up to 3000V will exist permanently on the
accessible PCBs which is LETHAL! Keep away of the parts on the PCBs!
Keep track that nobody could access the dangerous parts and do not
leave the amplifier without supervision during next adjustment period
with the top cover removed!
Connect a dummy load (or an antenna) to the output. Install all
cables to the exciter as usually. Now, feed mains voltage, turn on
the amplifier and let the tube at least 15 minutes in STANDBY mode.
Please guard the accessible HV parts during this period!
Select same bands (preferably lower) on both the amplifier and the exciter.
Use a small-size, flat-tip, insulated screwdriver for next
adjustments. On the MAINS PCB, find the two trimmer potentiometers
RP1 and RP2 (marked "BIAS1" and "BIAS2"). They control the idling
(zero-signal) plate current of the tubes for low- and high- RF-drive
levels respectively.
Please note that RP2 will affect both idling levels, while RP1 - only
the low level. That is why, the high level is adjusted the first, and
only then is set the low level (according to the procedure described
below).
b) Select the "Plate Current" information screen on the LCD. Go to
the OPER mode. Apply very small drive power in CW mode (1...5W).
Following the plate current, adjust R2 (BIAS2) to reach 220mA
(200...240 is OK); CCW rotation will increase the current. Don't
exceed 15 seconds with the PTT on. If you need more, repeat the
adjustment 1-2 minutes later.
c) Press the PTT but do not apply any drive during the adjustment of
RP1 (BIAS1). Select SSB mode, with the MIC and OUTPUT regulators on
the exciter set to minimum.
While monitoring the plate current, adjust RP1 (BIAS1) to set the
plate current to 70mA (60...80 is OK); CW rotation will increase the
current. This adjustment does not affect the previous step.
6. REASSEMBLING THE AMPLIFIER
After the adjustment procedure is completed, switch off the amplifier
and pull the amplifier power plug out of the mains wall outlet. After
five minutes or later, remove both "cover-presence" imitators. Do not
hurry to remove them since the residual voltages will be still high!
Do not touch any part inside during reassembling the amplifier, since
residual voltages may exist and the tube is still hot.
At last, install the top cover again as described below.
Be careful to align screws thread to the nuts and do not force them
since any captive nut on the chassis might be damaged.
a) Put the cover above the chassis, while holding its rear edge
slightly lifted (to 2-3cm). Align its horizontal and two vertical
front edges to the respective front-panel chutes. Then push gently
the cover forwards, in order to insert its front edges into the
front-panel's chutes. Take care especially to the bottom corners of
the cover.
b) Screw in loosely all 9 pcs of "eco-fix" flange-button head screws.
Use a Philips-2 screwdriver.
c) Pressing continuously the cover forwards and to the bottom,
tighten all 9 screws properly.
- End -
)
Сообщение от Lerik
