Nattawut Uamkruea, blogger and audio gear maker who passionate in vacuum tube, audio & music.
Producing electronics projects since high school. Seriously upgrade and modify vintage audio equipment for “Real Sound” concept.
He is a co-founder of Soundaries and Sentimental Studio, all audio solution provider.
Experienced and lively explore the listening rooms & audio shops in Japan as his most favorite to do.

Tuesday, November 24, 2015

Prepare Deck for Reel Tape Playback with "Tape Head" Feature in Vintage Preamplifier

Many top class vintage preamplifiers almost have "Tape Head" amplifier

with NAB equalization to use for commercial reel tape and cassette tape.

But some owners of those preamplifiers used to test or taste.

I will get some vintage preamplifiers to renovate and modify,

so I want to hear a sound of tapes from them too.  

I already have Technics RS-1700, 4 track reel to reel tape player and recorder.

But I kept it for a long time and some parts need to replace for promptly use.

Just order this service kit from ebay.

This set have 4 x brake pads, 2 x rubber belts for counter, 2 x bearing balls for tension arms.

First open back cover and remove capstan motor.

See 2 counter belts inside.

Remove reversing roller for take old counter belt out.

With new tighter belt.

Current tension rollers with corrosion. ;)

New rollers in their positions.

These brake pads are "must" need to replace.

Already remove and clean.

Use rubber adhesive glue for this job, match with vinyl and leather.

Replace with new pads.

Modify connectors to get direct signal from tape playback head.

Need to check and calibrate other points before using. 

Wednesday, November 18, 2015

Capehart Panamuse A-10 Amplifier Renovation Part 1

Radio/Phonograph console from 40's with field coil speakers.

"Panamuse" line had many models but almost use 2 chassis of power amplifier inside.

M-2 amplifier chassis called A-10:

9 tubes for 20 watt and two 12" "Precision tone loudspeakers" (Jensen).
Tubes: 6R7 phase inverter, 6C8G driver, 4 x 6V6G, 3 x 5Y3G.

M-3 amplifier chassis called A-9:

6 tubes for 10 watt for one 12 " speaker.
Tubes: 6R7 phase inverter, 6SC7 driver, 2 x 6V6G, 2 x 5Y3G.

More pictures in link below.

My friend have got 2 chassis of A-10 from ebay but had some different parts.

One chassis follow A-10 information above but other had 6J5 replace 6R7 position.

Different capacitors and the coolest part in 40's - Phase Splitter Autoformer. ;)

First one with 6R7, 6C8G and silver can autoformer.

Other with 6J5, 6C8G and black box autoformer.

Top view of 2 different chassis.

4 of 6V6G tubes in parallel push pull mode.

Parallel 5Y3G in rectify section.

Very old capacitor but still cool-looking until today.

Bottom view/ components inside.

All cloth wires from that day.

Almost wax capacitors were melt and capacitance had changed.

Old & cool style components layout on papers.

My friend need to renovate these amplifiers into new chassis and get rid of different parts.

Modify circuit both amplify and rectify sections

because of they had no field coil to use as filter choke and adapt to easily use in system.

Continue in part 2 after finish renovation these 75 year old amplifiers.

Thursday, November 12, 2015

My new WE tube amplifier with P&C transformer Part 2

Continue from part 1 that has built and tested for a month.

Single ended amplifier from Western Electric tubes and components,

using 421A double triodes tube as power, 418A tetrode tube as driver

and 394A thyratron tube as rectifier.

P609 output transformers with original WE core from P&C Electronics Japan,

Thordarson input transformers, WE 274 type inductors for filter chokes.

Designed for compact size in real wood frame.

Schematic of both channels that use ExpressSCH program for drawing.

WE421A has nice smooth sound, not too sweet but compromise with many kinds of music.

Similar 5998 Tung Sol with more mellow tone.

WE418A with triode connected support WE421A to get more energy

and same bulb & base like WE437A is a valuable appearance. ;)

2 of WE394A thyratron tubes work as full-wave rectifier,

Get both benefits from thicker sound of mercury-vapor & gas filled

and beautiful blue glow of bird cage style grid.

P&C P609 output transformers is a highlight of this amplifier.

They're deliver WE characters from using original core and improved frequency response

to cover music after WE era.

Reasonable price for people who need WE sound characters in their systems.

Flat non-inductive wirewound resistor from CTS with WE patents as cathode resistor of WE421A.

WE 274 type inductor as filter chokes, not hard to find and reasonable price.

Inductance and current rating quite low because of size limit

but enough for low watt SE amplifier or preamplifier.

Main power transformer from old transmitting equipment.

External filament transformer for WE394A tubes because they need more current than

main transformer winding can deliver, and inside area has no space to assembly. ;)

Using "Real" WE cloth wires for all wiring inside amplifier.

PIO capacitor and bleeder resistor across first electrolytic capacitor.

Rectifier area with Sprague oil filled, F&T and Hitachi HL2 capacitor.

West-Cap CPV09 paper & film in oil were selected as coupling capacitor.

Will bring Arizona capacitor "Blue Cactus" to replace this position and test again.

Wet tantalum capacitor as cathode bypass of driver tube for clearer sound.

Let enjoy with music along the night. ;)