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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 22nd February 2019, 07:34 PM   #901
6A3sUMMER is offline 6A3sUMMER  United States
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Join Date: Jun 2016
VictoriaGuy,

This thread has 900 posts. There have been several schematics, not all the same. I believe some in this thread have built their own amp, with various parts, just referring to the schematic (parts may or may not be the same). Others purchase the kit. But I believe there are at least 2 versions of the kit.

Fdlima has one version of the Boyuu amp. Is there more than one version? Were there any parts changes during the production run(s) of the Boyuu amp? How about any circuit changes of the Boyuu amp?

Getting different results only takes: One part change (self bias resistor, output transformer, tube rolling, UL tap was 40% but now is 50% etc.). Output mode change (UL, Triode, Pentode), Addition of negative feedback (and method: output tap to output tube cathode, output tap to driver cathode circuit, Schade feedback, etc.).

Most of these kit amps seem to have a circuit board; but that does not stop eager builders from making major changes.

And then there are tubes, weak tubes, tube ‘substitutes’ and Bogus tubes.

Apparently, some do get low power from (some versions of) these amplifiers.

For any amplifier that is not performing as the owner expects, there are lots of specifics that need to be known by anyone that would attempt to troubleshoot it via the internet.

I do not always write clearly. I also make mistakes. I said: “It sounds like the EL34 is triode wired.” Of course I can not “hear” what his amp sounds like. I should have said: “Perhaps you wired your amp in triode mode.”

My next post will address something about long threads.

Thanks to all on this forum who read, write, build, listen, and participate.
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Old 22nd February 2019, 07:51 PM   #902
6A3sUMMER is offline 6A3sUMMER  United States
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Join Date: Jun 2016
To the Moderators of this Forum:

I believe the rules state that we need to do a search before we start a new thread. That has several advantages: It reduces the amount of threads that come up in a search (easier to find what you want). It allows the many contributions on a subject or device, etc. to be in one place (one thread). I am sure many others can list other examples of advantages.

But there is another side as to whether or not to start a new thread:

Using this thread as an example (unless someone else puts up a post before I finish my edits, this will be post # 902).

My post 901 shows that unless you read through all the previous 900 posts, you may miss something. We do not all have the time to read through 900, and analyze each post, and then give help based on all of that to a new (late) “poster” who is having problems. And did that new poster read through all 900 posts so that we are all on the same page, so to speak.

And a late post may refer to a schematic, but which one? And is there a modification that is not in the schematic?

Starting with a new thread might make the person who starts that thread to be careful to give details, so we can start from there; instead of starting with some assumptions about posts 400 to 450 that similarly address the problem.

No, I do not really propose making it easier to start a new thread, but I am sure some get frustrated by not having a new one on a clean slate.

Does anybody have a solution?
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Old 22nd February 2019, 09:49 PM   #903
VictoriaGuy is offline VictoriaGuy  Canada
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Location: Victoria, BC
Boyuu EL34 A9 Tube Amp
Wow...I was just trying to help by posting the stock schematic.

Fdlima joined the thread at Post #768 so it is a while back, I admit.

"Have a good day."
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Old 23rd February 2019, 06:21 AM   #904
6A3sUMMER is offline 6A3sUMMER  United States
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VictoriaGuy,

Just keep helping. Thanks for that.

I am just a bit of a stuffed shirt. And I can be a control freak.
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Old 23rd February 2019, 03:21 PM   #905
VictoriaGuy is offline VictoriaGuy  Canada
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Location: Victoria, BC
Boyuu EL34 A9 Tube Amp
Thanks. It wasn't a big problem.
Around 'here' I see my small role as answering some of the very easiest questions, to free up the time of people like you to take care of the 'higher level' topics.
I'm sure it must be a bit tedious for experts to answer the same basic questions year after year, but it does help to engage beginners in the hobby.
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Old 11th March 2019, 02:23 PM   #906
Mariusduss is offline Mariusduss
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Default Little bit of help please

Dear all, First of all I will like to say that I appreciate all the work you put in this . Based on what I saw here I decided to buy myself this kit Boyuu A9. I was very excited when it arrived and I started the assembly and here is the point where the problems started. After assembly at first power on I have a huge HMMMMMM in both speakers. After reading the posts form here I could not fix it. I tried also the moods from VictoriaGuy but this also didn`t help. The only improvement was obtained when I put the 200 Ohms 3w resistors in parallel with C302. The HMMMMM was gone but the R301 started to get very hot ( it was so hot that started to smoke ). Any ideas are most welcome.

Thank you.
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Old 11th March 2019, 04:58 PM   #907
VictoriaGuy is offline VictoriaGuy  Canada
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Join Date: Dec 2008
Location: Victoria, BC
Boyuu EL34 A9 Tube Amp
Quote:
Originally Posted by Mariusduss View Post
The only improvement was obtained when I put the 200 Ohms 3w resistors in parallel with C302. The HMMMMM was gone but the R301 started to get very hot ( it was so hot that started to smoke ).
Any ideas are most welcome.
Hi!
Please see the schematic below...is this the one you are using?
I'm not sure exactly what you did (or why) but...

Putting a 100R or 200R resistor from the B+ high voltage rail to ground (bypassing C302) is definitely NOT a good idea. Some Ohms law and power calculations will show that..

So definitely remove that 'mod' as a first step.

Then, double-check your wiring against the schematic.

Next step for me would be to remove all the tubes (and the speaker), power up the amplifier and check for the right heater/filament voltages at the correct pins on the tube sockets. Use the AC volts setting on your meter.

You do know that the tube pins are numbered clockwise, looking at the bottom of the tube? -i.e. from the inside of the chassis- this is a quite common beginner mistake.

Report back with the heater voltages and pin#s, and post some pictures of your wiring, and somebody here will help.
Attached Images
File Type: jpg Boyuu A9 better rez stock schematic rotated .jpg (216.3 KB, 96 views)
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Last edited by VictoriaGuy; 11th March 2019 at 05:01 PM.
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Old 11th March 2019, 08:59 PM   #908
Fdlima is offline Fdlima
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Quote:
Originally Posted by Mariusduss View Post
After assembly at first power on I have a huge HMMMMMM in both speakers.
Hi Marius,

Welcome to the group. This group has helped me a lot and I have learned a lot from them too.

I had the same huge hum on both speakers when I first powered on my A9 amp and the problem was that pin 4 of the pre-amp tube needs to connected to pin 1. this connection is not shown in the diagram that comes with the kit. The loud hum should go away once you connect pin 4 with pin 1.

Let me know if this fixes the problem.

Frank
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File Type: png Screen Shot 2019-03-11 at 4.44.00 PM.png (246.7 KB, 78 views)
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Old 12th March 2019, 09:39 PM   #909
Kris Rocka is offline Kris Rocka
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Join Date: Dec 2018
Greetings Forum Family, I want to say thanks for a great read on this amplifier, it served as a very informative preamble. I purchased the kit on Ebay and assembled it incorporating a few mods that I gleaned from here including some component changes. The amp has been in use for the past 6 weeks with no issues.

It sounds wonderful playing a variety of program material through Klipsch RP-160M loudspeakers!
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Old 13th March 2019, 02:51 AM   #910
VictoriaGuy is offline VictoriaGuy  Canada
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Boyuu EL34 A9 Tube Amp
Quote:
Originally Posted by Kris Rocka View Post
The amp has been in use for the past 6 weeks with no issues.

Good work!
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