Retro Electronics and Audio Lab, Midland, TX. Updated 10/6/07
Retro Electronics Home Page
David Bogen HO 125 high powered PA amp repair journal (October 2007)
Older model David Bogen Challenger PA amp. This is a 35 watt amp using 2 6L6's for output.
View before restoration.
Bogen Challenger Amps. Shown
here are 2 CHB-35's and a CHB-20. The CHB-35's use 2 7868 tubes for
output and the CHB-20 uses 2 6BQ5's. John bought these while on
vacation and we have not tested them yet.
Front view, 3 amps.
PA amp with turntable.
Appears to be early 50's model...brand new in box, never used. It has a
vibrator power supply to use on 12 or 6 volt DC and a battery hook-up
cable, and can also be operated on 120 v. AC. Uses 2 6L6 output tubes.
We will replace old capacitors that have deteriorated through time.
Photos: Front view.
Operadio PA power amp.
1940's model: uses 4
6L6's, 2 5Z3's, an 80, and a 6SN7. Operadio later became the DuKane
corp. manufacturing similar equipment. This is really a military or
heavy industrial quality unit. We replaced all capcitors and installed
a new 6L6 to replace a missing one and a 6SN7 in place of the
mistakenly installed 6SL7. A new volume control was needed, and the
high-low line voltage switch was bad. The power transformer was wired
permanently in the "high" (120 volt) position...the "low" (110 volt)
position provided too high of a tube filament voltage, and most
locations today tend toward high line voltage.
We found that the audio was intermittently cutting out...this was
traced to the B+ fuse socket. Someone had installed a 15 amp fuse, so
we cleaned the socket contacts and installed a new 1/2 amp fuse.
We teamed up the Operadio with a Heathkit preamp, model WA-P1. We used
filament and plate voltages from the Operadio amp to operate it. This
preamp was recapped as well. Someone had put a 12AY7 in place of the
12AX7 phono preamp, causing weak sound on phono...replacing with the
correct tube brought back good sound.
One safety note: the original circuit of the WA-P1 connects the RCA
jack output directly to the plate of the 12AU7 tube, resulting on 110
volts on the RCA jack. We wired a .1 mfd 600 volt capacitor from the
12AU7 plate to the RCA cable for safety.
view of amp, turned on its side. Testing
new volume control. Testing
unit, rear view.
capacitors installed. Front
preamp with new caps.
Testing completed setup: View 1
Jose Tarango with completed amp. He reports it sounds great
with his guitar.
Silvertone P.A. Amp: John
replacing capacitors in a 1930's Silvertone amp This amp
originally was used in a film projector...it has a field coil
speaker in a cabinet with it. Finished
Sound-Reinforcement amp and mixer: uses 4 807 tubes for
output: part of our own collection. We use this amp to supply the whole
shop and and outdoor horn
with sound. All 3 jukeboxes are hooked up to it, along with a
microphone, AM/FM tuner, and Garrard 78 rpm changer. The switches on
are for turning specific speakers on and off: We are using a
70-volt distribution setup.
Mixer/Amp Front View, RCA
RCA 807 Amp set up and working:
amp CHB-10: uses 1 7868, 1 12AX7. We replaced the
cheapie ceramic coupling caps with mylars for better sound and
added a power indicator lamp.
CHB-10 chassis, Underside
of Bogen CHB-10
Unfortunately the paint sustained damage due to rough handling by
a previous owner.