Yamaha C-4 Preamplifier Input Knob Selector Repair

DIY DC/DC Dual Boost regulated Power Supply for High Voltage Tube VAS

In relation to DIY Hybrid amplifer the first step is to obtain the High Voltage for tube's anode supply and the low voltage for heaters.

Sometimes, if not always, fora a 100W amplifier you have a double sec 150-300VA  36-0-36Vac power transformer only.
Using this board you can adjust the  needed voltage for tube stage starting from your transformer.
Without use any voltage doubler and linear regulators.

The Following image shows how the Double Boost works.

From unregulated  +55/0/-55Vdc the circuit gives at his output the needed voltage, able to supply the anode current for a tube stage.

For example you can obtain +90/0/-90Vdc and 6.3Vdc for the heaters..

Yamaha AX-550 RS Amplifier 2SC3281 2SA1302

Restored Amplifier AX-550 RS

Working Condition

AX-550 RS Amplifier

AX-550 RS Amplifier ELNA for Audio Capacitors

AX-550 RS Amplifier ELNA for Audio Capacitors

AX-550 RS Amplifier ELNA for Audio Capacitors

AX-550 RS Amplifier ELNA for Audio Capacitors

YAMAHA A-1 AMPLIFIER NATURAL SOUND DIRECT DC, FROM 70's WITH LOOK Pt.II

Pt.II

No Fault!!! 

Every component is OK, power BJT are OK!!

So I put new main chord and give power.

Both channel have some volts of offset in their output and the idle current is too low.

So, following the Service Manual I can set the correct value of bias and offset trimmers.

Next step is to change the DISC lamp

VR1-VR2: offset voltage setting trimmer

Yamaha A-1

YAMAHA A-1 NATURAL SOUND AMPLIFIER DIRECT DC , FROM 70's WITH LOOK Pt.I

Not working Amplifier, Yamaha A-1 all Black metal.
I'm almost sure it is broken or it has big trouble because the main cable is cut.

Yamaha A-1

So I start, open the case.....wath I find is...Dust

Dust inside..

I remove dust from jewel...

Yamaha A-1 inside, without dust!!

Inside A-1 demonstrate his particular design, Two Power Transformers and two big capacitors.

Power amplifer circuit is splitted on 2 boards+1 an 2 Big Heat Sinks.

The input and VAS stage is a full of components board, there is also an other little board(+1) only for to mount  the Yamaha double n channel JFET 2SK100

Yamaha 2SK100  Y-K100 JFET

Next Step: let's find trouble!!!

My Sony ES HI FI system

About Sony:
Integrated Amplifier    TA-F555ES
Cassette Deck          TC-K777ES
CD Player                 CDP-701ES
CD Player                 CDP-501ES
CD Player                 CDP-502ESII

About Philips:
Speakers                  FB-821
CD Player                 CD-650

About TEAC:
Cassette Deck          V9000 Esoteric
Cassette Deck          V5000

About Yamaha:
Cassette Deck          KX-670

About Technics:
Turntable                  SL-1410