[Amps] Drake L-4B Power Supply Buzz

[Barry Kirkwood]

Drake L series amps are excellent. Would advise hanging on to it. If you
must sell it cheap, sell it to me. Will pay shipping on rf deck, you can
keep power supply.
Things I can be dogmatic about:
1. The buzz means Something is Wrong.
2. Wrong may be (a) trivial, or(b) serious.
3. Do NOT continue using power supply until fault is diagnosed.
4. Depending on nature of fault options : (a) Repair fault and do
maintenance on power supply. (b) build new power supply (c) both (a) and
(b).
5. To implement all options (4) decisions: (a) Do it yourself. (b) Get paid
or unpaid expert help (c) Some combination of (a) and (b)
6. HIGH VOLTAGE IS DANGEROUS. Unless experienced or prepared to spend time
learning about safety procedures do not embark on 5(a). 5 (b) is obvious. 5
(c) Using experienced guide means you learn things, maybe make lifetime
friend. Also has safety aspect. Although all of us have done it, it not good
practice to work on high volts gear without someone around with knowledge
about how to act safely if someone receives electric shock.
7. Taking  into account all of the above, it makes sense to pull the
existing power supply apart and diagnose fault. If there is serious fault in
transformer itself then options come down to making good existing
transformer or building complete new power supply.
8. If transformer itself OK or simple thing like needing laminations
tightened or wedge to pack any gap between windings and core, then  before
reassembly (a)  Replace all the filter capacitors, regardless. Unless they
have been replaced already they will be old and likely to break down. In
fact they may be the cause of your buzz. (b) Test all diodes and bleed
resistors . Consider replacing and upgrading all the diodes and resistors
with tested new ones of better specification, especially if even one
original shows fault or looks tired. The refurbished power supply should
give you years of service.
9 Once upon a time I had an early Drake L-4. Very good. Yes, the power
supply buzzed. By my standards the original supply puny, therefore built a
new power supply from scratch. New power supply bigger and stronger in every
respect. Cost? If you dedicate yourself to the search you will be able to
score a suitable transformer cheap. Just keep hunting. All other components
best purchased new, to highest spec you can find/afford. You can add small
luxuries like step start etc. The new power supply will not make your signal
significantly louder, but it will make it marginally cleaner due to better
voltage regulation.
So why go to the trouble? Think of the difference between a long journey in
a car with a big, high capacity, low revving engine, and a 1100cc four
cylinder. The latter will get you there as fast, the former will give you an
easy ride and with greater reliabliity. And here the analogy breaks down in
the big power supply's favour: The big one will consume no more fuel than
the little one.
73
Barry ZL1DD
PS My old friend ZL1AIH has done the same big bertha power supply exercise
on an L-4, and you can hear it when ZM1A is working contests.
B


-- 
Barry Kirkwood PhD ZL1DD
barry.kirkwood at gmail.com
NZ: 021 160 8999
Thailand 081 235 1556