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prezden 26th July 2013 10:30 PM

2 Attachment(s)
I've built this YAHA but can't get to work. :o
There is power going to the board but absolutely nothing happens. The bottom side is kind of messed up from changing some components when it didn't work.
I'm hoping someone can spot something that I'm missing and it's not another screwed up project :eek:

JonSnell Electronic 26th July 2013 10:47 PM

Sorry but have you a schematic or at least some information on it, or where we can find information on it please?

prezden 26th July 2013 11:08 PM

1 Attachment(s)
Here are the specs for it- thanks

Avro Arrow 26th July 2013 11:20 PM

Where did R5 go?

prezden 26th July 2013 11:39 PM

I thought R5 was optional. It's not on the photo of the finished amp. When I first built it I had R5 on the board and then took them off when it didn't work.

dfy 27th July 2013 12:22 AM


Originally Posted by prezden (
I thought R5 was optional. It's not on the photo of the finished amp.

Pretty sure it is on that photo. It's just not mounted on the board - it's one of the two resistors hanging in the air next to the tube socket.

prezden 27th July 2013 12:36 AM

ok I'll put 5 back on and try again


dfy 27th July 2013 12:44 AM

Also, I'm really not sure about that "mod" to the heater supply described in your PDF. The original YAHA article has this set up as a 300mA constant current supply. With the "mod" described in the first schematic in your file, it seems to represent a 1.5V voltage supply. That doesn't seem great to me, just like the resistor values are mixed up or something (do wait for a more qualified opinion on that though before randomly swapping parts - but the wiring diagram above the photo in your PDF seems to confirm my suspicion).

edit: Also, I think the red lines in the wiring diagram are meant to be wire jumpers. (some of those extra holes can also hold the R7/C3 mod) Those are not connected on your board at all! So, for example, your tube cathode isn't grounded, but completely floating.

edit2: The silkscreen on your PCB also seems strange. The slot that says R2L (next to the caps) would be the perfect place for R1R, and indeed the wiring diagram in the PDF seems to suggest that R1R should go there. (but from cap to ground, so you're still one hole off) That description/schematic/board/etc is just very inconsistent.

prezden 27th July 2013 01:49 AM

There seems to be a bare wire from the 2 ac connections. Any idea what that's all about?

dfy 27th July 2013 02:22 AM

What AC connections? :confused: This amp is supposed to run off 12V DC!
(The two bare wires are probably the GND connection from the audio input GND to power supply GND, as well as one of the switch connections (that one is 'live', i.e. at 12V, during operation though).

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