Yamaha A1 restoration 2021

[avionic]

Where, on this particular amp, is the best place to attach the negative lead to Ground?

Either one of the points marked " E " on that diagram above.


E = circuit ground (earth)

 

[Hifibythekg]

And given it’s particular design, what amperage should the mains fuse be. UK, so 240V, and options are 3A, 5A, 10A, 13A.

 

[Martin.Ca]

And given it’s particular design, what amperage should the mains fuse be. UK, so 240V, and options are 3A, 5A, 10A, 13A.

That's actually in the service manual... 800mA

 

[Hifibythekg]

Thanks Martin.
Yes, and those fuses are looking good as they are.
Sorry, I meant the fuse that goes into the mains plug. It’s fitted with a UK 3 pin mains plug that requires a fuse to be inserted for it to work.

 

[Martin.Ca]

Oh. That weird UK electricity. Why are there fuses in the plugs? Do you not have a circuit breaker panel in the house?

What did you use when you'd plugged it in before?

13A seems to be popular ... https://uk.yamaha.com/en/search/index.html?search=mains+fuse ... for your weird UK electricity.

 

[Hifibythekg]

Yes, UK homes have a fuse board in each dwelling. But most new appliances come supplied with a fused plug.
The amp is newly acquired and had a poorly wired plug attached that had a 5A fuse fitted..
The various amperages are regularly used here but there’s probably one that’s most appropriate to this amp’s specification and it’s as easy to fit the ‘correct’ one as a ‘wrong’ one before firing it up.

 

[Hifibythekg]

...just looked again at the service manual and found this, 7.5A.

Closest UK one will probably be a 10 amp though.

 

[Martin.Ca]

Or safer to under fuse than over fuse... Especially when still checking it out.

 

[Hifibythekg]

Thanks Martin. Yes, I just looked at the back of a fuse packet and I think it said 5A appropriate up to 1200W, so I'll start with 5A, which is what was in there originally, even though the amp was playing up the guy didn't say that it was blowing mains plug fuses.

 

[mbz]

Schematic shows F203,4 as 800mA slow blow/timed. These are on the secondary windings
so should remain 800mA. For the european model a 1.6A slow blow is included on the primary.
Back panel shows 450VA at 240V gives 1.8A, I'd stick with 1.6A slow blow, round down rather than up.

 

[Hifibythekg]

Powered up and it’s working. Sounds perfectly fine on some Realistic Minimus test speakers.


Probably need to scrub those test points, and some Bourns trimpots would make taking readings a more satisfying procedure. When DMM readings flicker one can’t be sure if the original trimpot is unreliable.


For measuring the power supply voltage please can anyone tell me how this is done? Is it like this...?

• set DMM to DC volts
• Red lead to TP1 black lead to Ground?
• Then red lead to TP2 black lead to Ground.

Where is the best Ground contact on this amplifier?

 

[Hifibythekg]

Schematic shows F203,4 as 800mA slow blow/timed. These are on the secondary windings
so should remain 800mA. For the european model a 1.6A slow blow is included on the primary.
Back panel shows 450VA at 240V gives 1.8A, I'd stick with 1.6A slow blow, round down rather than up.

Thanks MBZ.
Yes, although in the UK we also have a little fuse in the mains/wall plug. It’s that one I was wondering about. With a 5A fuse in the plug it didn’t blow on first outing.

 

[Martin.Ca]

View attachment 2346300 View attachment 2346300 Powered up and it’s working. Sounds perfectly fine on some Realistic Minimus test speakers.


Probably need to scrub those test points, and some Bourns trimpots would make taking readings a more satisfying procedure. When DMM readings flicker one can’t be sure if the original trimpot is unreliable.


For measuring the power supply voltage please can anyone tell me how this is done? Is it like this...?

• set DMM to DC volts
• Red lead to TP1 black lead to Ground?
• Then red lead to TP2 black lead to Ground.

Where is the best Ground contact on this amplifier?

F̶i̶g̶.̶ ̶1̶ ̶ ̶+̶v̶e̶ ̶t̶o̶ ̶T̶P̶2̶ ̶,̶ ̶-̶v̶e̶ ̶t̶o̶ ̶T̶P̶1̶ oops. Edit:--> -ve to E, +ve to TP1, TP2 in turn (yes, manual has some confusing bits)

 

[mbz]

in the UK we also have a little fuse in the mains/wall plug. It’s that one I was wondering about.

2A should be plenty

Where is the best Ground contact on this amplifier?

I like to use any black speaker post (common GND amps), often it's a clip type, eg, CA-1000, though the A-1 uses a screw
so you might find it a bit fiddly.

For measuring the power supply voltage please can anyone tell me how this is done? I

You can do it as per the service manual. If you have the base off then stand amp on side, some nice test points are then
accessable

 

[Hifibythekg]

Fig. 1 +ve to TP2 , -ve to TP1

Thanks Martin but, pardon me if I’m missing something really obvious, TP1 to TP2 only gives one readout and the manual shows two.. +35, and -35..?

 

[Hifibythekg]

Thanks MBZ.

 

[avionic]

TP1 to TP2 only gives one readout and the manual shows two.. +35, and -35..?

E to TP1 and E to TP2 ... The posted manual diagram is wrong..

 

[avionic]

For measuring the power supply voltage please can anyone tell me how this is done? Is it like this...?

• set DMM to DC volts
• Red lead to TP1 black lead to Ground?
• Then red lead to TP2 black lead to Ground.

Correct..

E to TP1 and E to TP2 ... The posted manual diagram is wrong..

 

[Martin.Ca]

E to TP1 and E to TP2 ... The posted manual diagram is wrong..

oops, yes.

 

[mbz]

My units are from the Japanese market, ie, early serial numbers. They only have the one bias TR, also TP2 is connected to GND.
Hopefully changed in later units.