Dynaco Mark III and IV Startup Procedure

I found a pair of Dynaco Mark III 60 watt amps
along with a pair of Mark IV 40 watt amps.

They haven't been used in ten years. They
worked when I packed them up.

Visual inspection doesn't reveal anything obvious.

Is there anything special I should do before
powering them up for the first time?

I'd like to put them back in service driving
a set of Dahlquist DQ-10 loudspeakers.

I ran across Dynakitparts.com recently, which
would make repairs possible if need be, but
I think I'd also like to improve them if possible.

Are there aftermarket upgrade boards for these
Mark III and IV models?

Most seem to focus more on the Stereo 70.

Isn't a Mark IV simply "half" of a Stereo 70
that produces slightly more power because the
power supply is not shared with a second channel?

-gb-

I always replace the original two wire line cord with a grounded cord before operating any tube amplifier. These tube amps all have metal chassis and grounding the chassis properly is a vital safety issue in my view. I have yet to encounter any hum issue from grounding the chassis. You usually have to enlarge the hole for the line cord to install a proper strain relief for a grounded cord. An IEC socket is also a possibility if you don't mind cutting a fairly large hole in the chassis. I usually use an attached cord for classic amps and an IEC socket for new builds.

Thanks Dan,

A very good idea. Will do.

-gb-

Thanks Bob,

Are you saying I can simply adjust the
bias to 1.08 volts and be good to go?

Or must I change the value of the two
13.5 ohm bias resistors?

-gb-

Thanks again Bob,

I powered up each of the four amps
individually last night on my bench,
and they all work! I was amazed.

Aside from a missing fuse holder cap
on one of the Mark IV units they've
all survived their long sleep.

I dug out a couple of Sound Valves
preamps to use with them and they
both work too!

Using a Sound Valves VT101i and the
pair of Dynaco Mark III amplifiers
I drove the Magnaplanars in my main
listening system for several hours.

I'd forgotten just how good VT gear
can sound. The Dynaco amps do not
drive the Maggies to the same SPLs
that my Rotel 200 wpc solid state
amp, but they're loud enough for me.

All four of my Dyna amps are stock.
I'm wondering if the aftermarket
upgrade driver boards will make a
noticable difference in sound.

I think I'm going to upgrade the
Mark III units first. I've found an
upgraded stainless steel chassis at
Triode Electronics that will give
me IEC power capability along with
punched openings for proper banana
connectors.

I have some questions about my PCB
upgrade options, but I think I'll begin
a new thread.

-gb-