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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
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Old 28th June 2018, 10:46 AM   #401
Mission720 is offline Mission720  United Kingdom
diyAudio Member
Join Date: Sep 2016
Location: London
Hi wishmasterX

I have the Boyuu A10 EL34 SE amplifier. This is point-to-point wired with 'Japanese' uprated power and output transformers. It would be easy to modify, but I have not had time or requirement to do so yet.

I have owned this for 18 months now, having bought fully assembled. It came stock with EL34 Shuguang tubes and 6N2 chinese double triodes and stock rectifier.

I am in the UK and the voltage is very stable, although I've not measured it at primary or outgoing of rectifier valve.

Without any modifications I have just dropped in EL34, EL34B, 6CA7, Shuguang 350C, 6P3P, KT77 and finally 6N3C-E and they have all 'worked' but I have not measured their performance.

I have also tried two different types of solid-state drop-in rectifiers with various valve combinations. When I have time I will check the o/p valve bias currents and also the various B+ and other voltages for each combination.

The power and output transformers have not got overly hot at all in any of the above configurations. They are warm to the touch after a few hours but that's all.

Hope this helps.
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Old 7th July 2018, 03:56 PM   #402
JohnnyEcho is offline JohnnyEcho
diyAudio Member
Join Date: May 2018
Default Boyuu A9 Builder Looking For Help

Hi All

After Watching All The Fun You Are all Having Building The Kit, I Took The Plunge And Bought One.

Now All Went Well Until I Came To Test It, (apart from pins 1 & 4 on the input tubes not shown as linked on the schematic, Picked that up from your forum)

First I Had A Very Loud Hum/Buzz On Both Channels, After Checking Everything And Moving The Heater Supplies Away From Any Input Wires/Pins, It Did Reduce.
My Problem Is That I Still Have Quite A Loud Hum/Buzz But As Soon
as Any input signal is connected, the amp plays it at full volume, regardless of the volume position.
almost as if i have built a super sensitive amp?
I have checked the volume control and it's working as it should, (checked with my calibrated fluke).

Has anyone got any ideas?
Anything Considered.
I'm Confident with electronics and have built many electronic kits but this is my first valve project.

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Old 7th July 2018, 10:10 PM   #403
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
Join Date: Jun 2016
Sounds to me that one or the other of the RCA phono connector input ground, bottom of the 100k Ohm volume pot, and the common ground of the amp are not all connected together.
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Old 8th July 2018, 02:24 PM   #404
JohnnyEcho is offline JohnnyEcho
diyAudio Member
Join Date: May 2018

Thanks For Quick Reply, You Were Spot On.

After Checking Out The Volume/RCA input lines, Found A Dry Joint At The RCA Circuit Board Ground To RCA Socket Grounds.

Only Found It By Measuring Between Ground on RCA Circuit Board And RCA Sockets Outers On Rear Panel.

Looks Like I Made The Joint Good When I Pressed The Probe Of My Meter On It, While Testing It?

Anyway Now My Amp Is Working Almost Perfectly.
I Do Have A Slight Buzz You Can Only Hear At Very Low Volume Or Quite Sections in-between Tracks.

I'll Have Another Go After Its Settled In Awhile.

Thanks Again, Your Help Is Greatly Appreciated.
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Old 14th July 2018, 07:59 PM   #405
kirtbynoe is offline kirtbynoe
diyAudio Member
Join Date: Sep 2010
Hello All,
After reading and re-reading this thread (very informative but soooo long), many thanks for all the valuable info and knowledge thats been contributed. I'm just about to start a build on an A9. I want to incorporate the mods by Geek Stuff. Does anyone have an opinion of what order to follow for the build? I'm thinking that I would wire in the components on the PCB first then the coax, followed by the transformer, AC, B+ etc. and finally the components from the valves to the PCB. Any help would be gratefully accepted. If I've missed this somewhere in the thread please forgive me.
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Old 18th September 2018, 08:14 AM   #406
BobDraper is offline BobDraper
diyAudio Member
Join Date: Jun 2016
Can anyone help me?
I finished my Boyuu A9 in accordance with the schematic and the help of a photo of the completed amp circuitry. There is a very loud hum a few seconds after switch on. All the heaters light up. The amp produces output when the volume is turned up. When I switch it off the hum disappears immediately and the sound continues for a short while.

Someone on youtube describes an identical problem. He got 3 engineers to look at his amp. The third one found the schematic to be wrong and fixed it. Does anyone here know what this error in the schematic is?

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Old 18th September 2018, 06:55 PM   #407
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
Join Date: Jun 2016
I believe there are more than one variation of schematics for this amp out there.
You may want to post .your. schematic on this thread.
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