Hi.
I've just ordered this kit and have been reading through the thread.
I'm interested in the Alps rk27 potentiometer you used.
What's the resistance? 50k? 100k?
Thanks in advance.
Re: Resistors required
Hi Nick,
Just north of Port Stephens - you are almost in my backyard. I am in Elizabeth Beach 25klm south of Forster.
I may be able help you with the parts that you need. I have on order a number of parts which are presently on a slow boat from China.
Place a photo of the engine room of the amp on this site and when I receive the parts I will let you know (initially via this site) if I can help.
Hi Nick,
Just north of Port Stephens - you are almost in my backyard. I am in Elizabeth Beach 25klm south of Forster.
I may be able help you with the parts that you need. I have on order a number of parts which are presently on a slow boat from China.
Place a photo of the engine room of the amp on this site and when I receive the parts I will let you know (initially via this site) if I can help.
A fresh victim. 
Greetings folks. I've just finished reading this thread, and have started reading 'Building Valve Amplifiers' in preparation for taking on an A9 build. I have lots of experience with digital electronics (and some analog I/O) and learned enough RF and analog to pass Element 3 35 years ago, but this will be my first foray into tube audio.
The included schematic matches VictoriaGuy's post #900, with the exception of finally showing pin 4 on the input tubes connected. My first thought was to build the amp as drawn on the included schematic to start, but it seems pretty clear from reading this monster of a thread that some initial mods are worthwhile. As such, I'm considering the following changes right off the bat:
As for bonding the two grounds, PrebenDK's schematic shows signal and chassis grounds bonded at the power transformer housing, but earlier discussion suggested a parallel R and C to bond grounds. What's current thinking on that arrangement?
I'm thinking that I'll save the output mode switch until after I have a working amp, and probably better speakers, unless there's a good reason to do that wiring now?
Greetings folks. I've just finished reading this thread, and have started reading 'Building Valve Amplifiers' in preparation for taking on an A9 build. I have lots of experience with digital electronics (and some analog I/O) and learned enough RF and analog to pass Element 3 35 years ago, but this will be my first foray into tube audio.
The included schematic matches VictoriaGuy's post #900, with the exception of finally showing pin 4 on the input tubes connected. My first thought was to build the amp as drawn on the included schematic to start, but it seems pretty clear from reading this monster of a thread that some initial mods are worthwhile. As such, I'm considering the following changes right off the bat:
- Separate grid stoppers and cathode resistors with bypass caps per Fdlima's schematic in post #1082.
- Virtual center tap on the 6.3VAC secondary for the input heaters.
As for bonding the two grounds, PrebenDK's schematic shows signal and chassis grounds bonded at the power transformer housing, but earlier discussion suggested a parallel R and C to bond grounds. What's current thinking on that arrangement?
I'm thinking that I'll save the output mode switch until after I have a working amp, and probably better speakers, unless there's a good reason to do that wiring now?
Help Requested
Hi Nick,
I replied to your post May 19th. As I stated in that reply you are almost in my backyard and I can likely help you out. Read that reply for more info.
Cheers,
Bob
Hi Nick,
I replied to your post May 19th. As I stated in that reply you are almost in my backyard and I can likely help you out. Read that reply for more info.
Cheers,
Bob
Sorry for budding in, but the artificial center tap can be achieved by adding a 100-250R resistor to the heater pins and grounding their ends.
I'll be adding a hum trim pot (humdinger) instead and grounding its wiper.
What I want to know is if instead of grounding can I connect them to the cathode pin for the elevated voltage "trick" and would that work on these amps?
I'll be adding a hum trim pot (humdinger) instead and grounding its wiper.
What I want to know is if instead of grounding can I connect them to the cathode pin for the elevated voltage "trick" and would that work on these amps?
Thanks. I understand. What you're doing is this (in the attached schematic labelled 'PRIMITIVE').
Yes, that will work.
It is not the best way to wire an AC heater supply.
Adding resistors to that type of circuit will do little to nothing to reduce noise from the heaters.
The better way is with two resistors connecting from either end of the secondary winding to ground, creating a resistive center tap for the primary winding. Merlin B calls this an "Artificial Centre Tap":
I got that from Merlin's excellent page on Heater Supplies. The page is written for people who want to design tube (valve) guitar amps, but the concepts for a hi-fi power amp are exactly the same.
The Valve Wizard
Read that, and you should come away with a much better idea of what's going on in your Boyuu amp.
--
I was just reading up on Humdingers, and the recommendations seem to be to connect to a divider to lift the heater to 45-60V, not all the way to cathode voltage.
No practical experience yet, as you can tell from my earlier post, I just happened to be reading about the subject this morning.
Hi everyone... A big thankyou to everyone for all of the information in here, what a thread !
I bought one of these (built) back in Jaunuary as my first tube amp and I've been slowly going through this thread and trying to learn as much as I can. The plan is to modify (butcher) this one as a learning platform, I have very little experience with electronics, before building my own.
So far, I've replaced the coupling capacitors with 0.47uf 400V and C302 with a 330uf 450V one as well as swapping out the volume pot (Alps 100k) and power switch (Lorlin). all going well and loving the sound using EH 6CA7 and Tung-Sol 6SL7GT with a JJ 5U4GB rectifier.
I'm going to add the artificial center taps to the 6.3v heater lines with 4 100R 3W resistors and rewire the heater filaments while I'm at it.
Also going to add a couple of 200K 2W bleeder resistors and a 3.3K 2W grid stopper to each 6SL7.
The last planned mod is a UL / Triode switch. As I only need 1 set of RCA input I've put a DPDT switch where the input button was and will wire this up to swap between modes.
Beyond this, I'm looking at the cathode bypass capacitors as covered in this thread and maybe swap out the resistors for some higher quality ones as done by Gidu.
This is where my problem is.... I've measured the resistors in my amp and checked the coloured bands so I know the values but I can't work out how to choose the right power rating and I'm hoping that someone on here maybe able to validate my choices before I buy anything. These are all Vishay metal film.
R102/202 - 470R 1W
R103/203 - 100K 2W
R104/204 - 2K 1W
R105/205 - 330K 1W
R106/206 - 100R 2W
R107,108/207,208 - either 4 x 1K 2W or 1 x 500R 6W
Thanks in advance for any help and I'll put some pictures up when I get the amp back together.
I bought one of these (built) back in Jaunuary as my first tube amp and I've been slowly going through this thread and trying to learn as much as I can. The plan is to modify (butcher) this one as a learning platform, I have very little experience with electronics, before building my own.
So far, I've replaced the coupling capacitors with 0.47uf 400V and C302 with a 330uf 450V one as well as swapping out the volume pot (Alps 100k) and power switch (Lorlin). all going well and loving the sound using EH 6CA7 and Tung-Sol 6SL7GT with a JJ 5U4GB rectifier.
I'm going to add the artificial center taps to the 6.3v heater lines with 4 100R 3W resistors and rewire the heater filaments while I'm at it.
Also going to add a couple of 200K 2W bleeder resistors and a 3.3K 2W grid stopper to each 6SL7.
The last planned mod is a UL / Triode switch. As I only need 1 set of RCA input I've put a DPDT switch where the input button was and will wire this up to swap between modes.
Beyond this, I'm looking at the cathode bypass capacitors as covered in this thread and maybe swap out the resistors for some higher quality ones as done by Gidu.
This is where my problem is.... I've measured the resistors in my amp and checked the coloured bands so I know the values but I can't work out how to choose the right power rating and I'm hoping that someone on here maybe able to validate my choices before I buy anything. These are all Vishay metal film.
R102/202 - 470R 1W
R103/203 - 100K 2W
R104/204 - 2K 1W
R105/205 - 330K 1W
R106/206 - 100R 2W
R107,108/207,208 - either 4 x 1K 2W or 1 x 500R 6W
Thanks in advance for any help and I'll put some pictures up when I get the amp back together.
From what I've been studying and from your link, I think this can only be applied to cathode followers - ours is an anode follower.
But we can still ground them.
Hey guys,
In anticipation to my A9 arriving by slow train, I've been reading the forum and collecting upgraded bits 'n bobs.
Early on, I ordered a 470uF/450V beast of a cap for C302 and two 33uF/450V for C301 and C303..
Are these overkill or potentially damaging to the rectifier tube or transformer?
I've been trying these out in LTspice and they seem to be working fine..
Also, does anyone know how many Henries in the Power and Output transformers or direct me to an earlier post?
Thanks in advance.
In anticipation to my A9 arriving by slow train, I've been reading the forum and collecting upgraded bits 'n bobs.
Early on, I ordered a 470uF/450V beast of a cap for C302 and two 33uF/450V for C301 and C303..
Are these overkill or potentially damaging to the rectifier tube or transformer?
I've been trying these out in LTspice and they seem to be working fine..
Also, does anyone know how many Henries in the Power and Output transformers or direct me to an earlier post?
Thanks in advance.
Thanks Daniellu,
I spotted the typo on R102 but can't seem to be able to edit posts. I've been reading up on Ohms law as well and I understand how to calculate the power rating I need for each of these so I'm happy with them now.
I've decided to ditch the pcb and rebuild the whole thing from scratch.... power and heater wiring done so far but I'm going to replace C301 and C303 (no change to values just new caps).
Attachments
Hi Bobbie, I just found your reply, cheers and I PM'd you many thanks, Nick
Hi Nick,
If you could load/show a photo of the engine room of your amp it would be helpful.
Attachments
Last edited:
The photos came thru. You did well Nick. However, your amp is not a Boyuu A9.
Take a look at all the images posted on this particular forum and you will see what an A9 looks like.
Does your amp have a name? Maybe you could find a forum for that amp elsewhere on this site!!
Cheers,
Bobbbie
Rebuild
Finished....
Got the last bits connected up this morning. Spent a bit of time measuring voltages and checking nothing started to smoke.....
Happy with the results so popped in the tubes which came with the amp and it works like a beauty. Not switched to Triode mode yet, just loving the sound after having to use my laptop to stream music for the last few weeks.
I couldn't have done any of this without this thread so thanks to everyone....
Finished....
Got the last bits connected up this morning. Spent a bit of time measuring voltages and checking nothing started to smoke.....
Happy with the results so popped in the tubes which came with the amp and it works like a beauty. Not switched to Triode mode yet, just loving the sound after having to use my laptop to stream music for the last few weeks.
I couldn't have done any of this without this thread so thanks to everyone....
Attachments
Re: Missing PCB
Hi, I was considering doing a revamp of my unit without the PCB. After seeing your work I may well go ahead sometime. Looks more 50's era.....
Any chance of a schematic showing all the mods to the original.
Cheers,
Bobbie
Finished....
Hi, I was considering doing a revamp of my unit without the PCB. After seeing your work I may well go ahead sometime. Looks more 50's era.....
Any chance of a schematic showing all the mods to the original.
Cheers,
Bobbie
Hi DIYBobbie/Ryan,
I went through all the posts here about 3 times , I can tell Ryan's Amp is A10. very similar to A9(apart from voltage amp stage). I would replace R107/108 (R207/208) with a single 470ohm 5w (or 6w), it's easy to go to Jaycar to pick up two. I don't know if there is other underlying issue caused this overheating problem, but it's a good start.
I went through all the posts here about 3 times , I can tell Ryan's Amp is A10. very similar to A9(apart from voltage amp stage). I would replace R107/108 (R207/208) with a single 470ohm 5w (or 6w), it's easy to go to Jaycar to pick up two. I don't know if there is other underlying issue caused this overheating problem, but it's a good start.