A brand new tube amp for under $100? - Nahhh...
- Thread starter aussiedan
- Start date
Gary Indiana
Active Member
From the "dissection" in here looks like four dropper resistors around 3,3 Ohm 2 Watts each in series with each tube's heater should do the trick.
Last edited:
aussiedan
Ambition beyond ability
No, not when I paid just under $500 for a Pioneer SM-G204.
I expected a hybrid amp, as advertised.
aussiedan
Ambition beyond ability
That sounds pretty simple. I should be able to do that. Will it matter if I put them on pin 4 or 5, and is there any particular type I should use over another?
Also, thank you Gary, for your help and being positive about the little china girl.
There is usually someone on AK that can help more than the knockers.
Danny.
Gary Indiana
Active Member
Pins 4 & 5 are the heater. It doesn't matter to which of these you'll connect the resistor. You might use pin 5 because being in the very middle it is easiest to locate without mistake. Any type of resistor is good: 2 Watts or more, they will get warm to the touch so don't let them rub against electrolitic caps.
Your amp is fine and might sound great with its tube stage and toroid transformer in the power supply. She has good looks and good connectors. People just got ticked off at the original false advertising. Which is nowhere near the famous Golmund vs. Pioneer ripoff.
aussiedan
Ambition beyond ability
Hi Gary,
It is already a nice sounding unit, the tubes are doing something more than just looking good, I am just concerned about its lifespan. I will get some resistors, then brush the dust off the soldering iron.
It is a pity it lacks a phono stage, thats my biggest dissapointment.
The dissection explains a lot of things, but, in closing he also states that the problem was bought to the attention of a local magazine, they approached the supplier and the problem was quickly rectified. And he got his money back:thmbsp:. No problem.
Good luck if you were to try that on an E-auction site, or taking your 6000 pound Golmund back because you heard it could be a Pioneer.
It looks like "badge engineering" is here to stay.
Thanks,
Danny.
Gary Indiana
Active Member
Simple phono preamps are available in kits. Dick Smith folks should be able to tell you who still sells kit sets in Australia.
Or, a couple of preamps (one for each channel) like these could do it.
aussiedan
Ambition beyond ability
Hi Gary
I wasn't aware a microphone pre could be used for phono. Cool, that opens up a few more avenues. Both Dick Smith and Jaycar have them. They start arround $20 for a kit, and up from there.
If china girl had a reasonable phono, I could put it into a bit of a rotation. I'll consider an extra box as time goes by.
Well Gary Indiana, the knockers might get the last laugh. I don't know what to think. The chassis is very solid and well built, but the electronics....maybe ok, but the boards look like all the green laquer is comming off. Another dissapointment is the lavish use of adhesive to secure the controls :thumbsdn:. The pretty little tube protectors also hold the circut board in place. At least each tube protector had one tight nut. They could have all been loose - gotta look on the bright side.
Anyway, my thoughts drifted toward a single dropper. I dont know if its viable, but its going to require removal of the tube mount (or one leg, anyway) to get a resistor in series with pin 5 on each tube. At least thats the only way I can see to do it neatly. I have the resistors (expensive at $0.88 each, when $0.10 is dear!), but I thought it may be easier to splice into the white connector wire (loom?), I think the centre wire may be the one. Would this be possible, and what sort of dropper would be used here (that is, are resistors still suitable here)?
I hope I have explained my question properly.
The pink rectangles are jumper wires, maybe where resistors should have been?
Yellow ellipse is some free corrosion. I love little bonus's
Green arrows are where I was thinking of desoldering and connecting resistors. This is where I was starting to feel the warranty voiding. Not sure if I'm doing the right thing here.
Whats your, or anybodys, thoughts?
Thanks, Danny
Attachments
Gary Indiana
Active Member
Hi Danny,
Informative post and great pictures! Good thing you looked inside your amp. It is still a good amp and should serve you well, although probably it's not "the best in its class"
The PCB isn't good quality, but it shouldn't really cause you any problems. The "rusty" spot looks like soldering flux which you should be able to wipe off with a Q-tip dipped in rubbing alcohol if it bothers you. The jumpers provide a couple of good spots for your series resistors to put in. But you will need to cut a couple of traces for the other two resistors to properly connect them in series with the two other heaters.
If you are not comfortable with cutting traces, then you might wait until your warranty expires and do it then, although by that time your heaters will get a lot of abuse (overheating), so that's your call. Below are pictures where the traces should be cut for your two resistors and which two jumpers should be replaced by resistors - remember they will get hot, so keep them away from electrolytic caps - and bottom (green side) of the board might be the best place to solder in the resistors. You might even leave their legs full length.
Your preamp kit, to work with phono, must be for dynamic microphone and not for electret (or condenser) microphone. Dynamic mic gives signal resembling that of a magnetic cartridge. You could put it right inside your amp with two additional RCA phono sockets and a grounding post - which obviously would kill your warranty for good.
Here is the heaters mod (new resistors in yellow) in your pictures:
This below might be a better alternative (you decide) for this half of the board:
This side of the board will require one cut trace:
Informative post and great pictures! Good thing you looked inside your amp. It is still a good amp and should serve you well, although probably it's not "the best in its class"
The PCB isn't good quality, but it shouldn't really cause you any problems. The "rusty" spot looks like soldering flux which you should be able to wipe off with a Q-tip dipped in rubbing alcohol if it bothers you. The jumpers provide a couple of good spots for your series resistors to put in. But you will need to cut a couple of traces for the other two resistors to properly connect them in series with the two other heaters.
If you are not comfortable with cutting traces, then you might wait until your warranty expires and do it then, although by that time your heaters will get a lot of abuse (overheating), so that's your call. Below are pictures where the traces should be cut for your two resistors and which two jumpers should be replaced by resistors - remember they will get hot, so keep them away from electrolytic caps - and bottom (green side) of the board might be the best place to solder in the resistors. You might even leave their legs full length.
Your preamp kit, to work with phono, must be for dynamic microphone and not for electret (or condenser) microphone. Dynamic mic gives signal resembling that of a magnetic cartridge. You could put it right inside your amp with two additional RCA phono sockets and a grounding post - which obviously would kill your warranty for good.
Here is the heaters mod (new resistors in yellow) in your pictures:
This below might be a better alternative (you decide) for this half of the board:
This side of the board will require one cut trace:
Last edited:
aussiedan
Ambition beyond ability
I'm not really worried about the warranty, I have technicly voided it by removing the cover.
I had a feeling the jumper wires may have been useful. I have difficulties with de-soldering. I can do it, I just dislike it. I didn't like the look of pulling the bases.
Should I cut the trace with an "exacto" knife?
I have not had to cut traces on purpose before (I just lift them de-soldering!)
The power switch area was a chinese puzzle. The trick was finding the right length screwdriver to reach the hidden screw (not visable) on the power switch. The studs are locked by another nut (inaccessable) under the board, making them fixed until the board is out. Note the glue.
I had a feeling the jumper wires may have been useful. I have difficulties with de-soldering. I can do it, I just dislike it. I didn't like the look of pulling the bases.
Should I cut the trace with an "exacto" knife?
I have not had to cut traces on purpose before (I just lift them de-soldering!)
The power switch area was a chinese puzzle
. The trick was finding the right length screwdriver to reach the hidden screw (not visable) on the power switch. The studs are locked by another nut (inaccessable) under the board, making them fixed until the board is out. Note the glue.Attachments
dsndblm
Super Member
EXACTLY why I would never buy one. I buy and use a lot of different products in my maintenace dept at work. Due to changes in our manufacturing and buying here in the states I'm stuck with over seas junk. Items that were made here lasted years. We are lucky if the new junk makes it through the job at hand. I'm forced to buy three times what I used to because one of three items won't work right out of the box. Sorry for the rant and tangent from tube audio. This one just struck a nerve
Gary Indiana
Active Member
Jumpers with two solder points are easy to remove without damage to the traces, use pliers to lift them off - don't burn your fingers.
Exacto knife, or any surgical blade, or a sharp box cutter will work perfect, all you do is run the knife's tip across the said trace, then second time parallel to it. Only a tiny gap (<1mm) is needed. Check with ohm meter if the trace is really open.
The resistors would be best placed on the bottom (green) side of the PCB.
Pictures below show revised (easiest) way to do this with only one trace cut:
Gary Indiana
Active Member
Exactly! Today very often I find better quality stuff at thrift stores and flea markets than the "brand new" crap at the stores. Although technology gets obsolete real fast.
aussiedan
Ambition beyond ability
EXACTLY why I would never buy one. I buy and use a lot of different products in my maintenace dept at work. Due to changes in our manufacturing and buying here in the states I'm stuck with over seas junk. Items that were made here lasted years. We are lucky if the new junk makes it through the job at hand. I'm forced to buy three times what I used to because one of three items won't work right out of the box. Sorry for the rant and tangent from tube audio. This one just struck a nerve
It is your choice how you spend your money, but you may miss out on some good sound for low bucks.
The unfortunate thing is the 3 imported ones all together were probably still cheaper than the 1 local one.
I only use top quality tools for my work (in maintainence myself). German and Japaneese ones seem to give exellent service at a mid to high price. I cannot stand boys toys for mans work. USA makes the best welders in the world, IMO.
I only do the occasional bit of woodwork at home, so I cannot justify $270 for a makita belt sander. I sand things with an $80 china made/italian branded thing. I can tolerate its shortcomings as I'm not using it to earn money.
The fact that Valve amp's one only lasted three days has helped prompt me to try and fix it. I hope I get more than that.
aussiedan
Ambition beyond ability
I have to get it up and running properly first.
Tubes are 6N1-J and 6P15.
Any suggestions on what tubes to try?
These ones are the Star and Lines brand, with some Chinese symbols.
Gary Indiana
Active Member
After the mod check the the voltages across heater's pins 4 & 5. It should be 6.3 Volts or real close to it. The dissection page said heaters run on AC, so a true RMS meter would be very helpful - try to borrow one since these meters are more expensive to buy.
aussiedan
Ambition beyond ability
I have neither a RMS multimeter or a CRO. I thought I'd just check it by running it and seeing if it helps.
Gary, I'm glad to say it has helped a lot. The 2 6P15's seem to be running nicley. The 2 6N1's still seem a bit bright, particularly the little guy on the left.
I also should have taken the voltage of the LED for the power, it needs a resistor or something to dull it down.
I am enjoying some Pink Floyd at the moment from CD. It sonds really nice. It does have some noise when running the phono from the "rec" of another tube amp
Could be an earth issue, as it has no ground terminal.
Anyway, thank you for your help. Without it I doubt I could have done it.
The countdown is now on for how long till it stops.
Danny.
Gary, I'm glad to say it has helped a lot. The 2 6P15's seem to be running nicley. The 2 6N1's still seem a bit bright, particularly the little guy on the left.
I also should have taken the voltage of the LED for the power, it needs a resistor or something to dull it down.
I am enjoying some Pink Floyd at the moment from CD. It sonds really nice. It does have some noise when running the phono from the "rec" of another tube amp
Could be an earth issue, as it has no ground terminal.
Anyway, thank you for your help. Without it I doubt I could have done it.
The countdown is now on for how long till it stops.
Danny.
Attachments
Gary Indiana
Active Member
Great job putting it all together, and the little amp looks sharp. A series 10 kOhm 0.25 Watts should dim the LED nicely.
If you get a couple more 3.3 ohm resistors (same type) you could add them in series with the smaller tubes' heaters. Like the turquoise color ones in the pics below. You might be able to genty pry the jumper with a small screwdriver while applying the soldering iron from the other side - without removing the whole board again.
