Cheap Chinese 6P3P kit

Oh Bob, you didn't tell me you swapped a pair of 807. The power of transformer is not enough for 807, it needs more plate current.

I think I just blew the transformer in this amp. I swapped in a pair of 807 tubes with socket adapters. After about 5 minutes the 5Y3 had a fire inside the tube which I caught after about 10 seconds, powered off. Took out the 5y3 swapped in the 5Z4 and put the 6L6 tubes back in and the amp worked for about 30 seconds and the tranny started to smoke. Damit. Looks like I'm going to need a new transformer. Is there a good one for this setup from Edcor/ Angela that someone can recommend?? Looks like I will have a challenge with size of a new one but I would be grateful for any suggestions.

I tried the 807s before with the 5Z4 rectifier and didn't have any issues. The rectifier looked like it went into thermal runaway ... fire inside the tube..Maybe 807 tubes not a good match for the 5Y3. ?? What else may I have blown?

Cheers,
Bob
 
Oh Bob, you didn't tell me you swapped a pair of 807. The power of transformer is not enough for 807, it needs more plate current.

Prior to the 807 I was running Sovtek 6L6WXT+ for 2 weeks.

I think it's not the output tubes but a short in the primary winding of the transformer (smoke coming from that location). I should be able to verify this testing the transformer out of case.

Here's a summary of the different tubes in question here. Note that the 6L6WXT+ is a 6L6GC maybe a little more (35W max output).

Absolute Max ratings:
6L6 - 22.8 watts
6L6GC - 33 watts
807 - 25 watts

I'm getting a new transformer and some new output transformers. When I get the new gear I want to triode strap the output tubes to see if this will indeed improve the sound.

Cheers,
Bob
 
Prior to the 807 I was running Sovtek 6L6WXT+ for 2 weeks.

I think it's not the output tubes but a short in the primary winding of the transformer (smoke coming from that location). I should be able to verify this testing the transformer out of case.

Here's a summary of the different tubes in question here. Note that the 6L6WXT+ is a 6L6GC maybe a little more (35W max output).

Absolute Max ratings:
6L6 - 22.8 watts
6L6GC - 33 watts
807 - 25 watts

I'm getting a new transformer and some new output transformers. When I get the new gear I want to triode strap the output tubes to see if this will indeed improve the sound.

Cheers,
Bob

There's a good chance the 6L6WXT+ is what cooked the tranny, and the 807's just finished off damage that was already done.
 
There's a good chance the 6L6WXT+ is what cooked the tranny, and the 807's just finished off damage that was already done.

The 6L6WXT+ tubes ran fine for a few weeks, tranny wasn't hot just a tad warm as expected. The problem started in the rectifier with smoke coming from the primary winding and still does after I unhooked the circuit. Can I measure the resistance on the tranny out of circuit with no power?

Cheers,
Bob
 
It's hard to say for sure what cooked the power tranny.
(but I believe this amp was designed for the "6L6" correct) ?

The 6L6/807 draw same heater current an should draw the same amount B+
current as well, if the power tranny didn't have much margin on those there
windings surely could have stressed the tranny enough that with an rectifier
meltdown took it over the top, yes generally an fuse should go but not every
time and or catch it in time either.

Now you got extra voltage on this tranny and setup so with using a specified
cathode resistor you may have drawn "extra B+ current" this tranny was not
over spec'ed for, but to me with voltage supplied by the transformer supplied
with an kit it should handle what the amp does when built to there schematic.

It could of also just been an rectifier tube itself died prematurely an took out
the power transformer from over current draw during the meltdown, now with
an defense to the kit manufacturer I would not expect much over ratings with
parts supplied in these cheap kits, not saying there tranny should blow on you
but if an over current situation arises I would not expect much headroom here
and a tranny could blow because it just isn't that beefy to start with.

If that transformer just died out of normal running with any 6L6/807 without an
rectifier malfunction I would say the kit had a bad/undersized rating transformer.
(but with a catastrophic rectifier failure can't say what the fault was)
 
The 6L6WXT+ tubes ran fine for a few weeks, tranny wasn't hot just a tad warm as expected. The problem started in the rectifier with smoke coming from the primary winding and still does after I unhooked the circuit. Can I measure the resistance on the tranny out of circuit with no power?

Cheers,
Bob

If you've got smoke coming out the PT with nothing hooked up not much reason to measure anything.
(it's cooked)

But yes the high voltage windings should have something like 25-45 ohms of resistance from an center
tap to each outer winding, the filament taps should be say 1-4 ohms, pretty hard to see filament short.
 
Prior to the 807 I was running Sovtek 6L6WXT+ for 2 weeks.

I think it's not the output tubes but a short in the primary winding of the transformer (smoke coming from that location). I should be able to verify this testing the transformer out of case.

Here's a summary of the different tubes in question here. Note that the 6L6WXT+ is a 6L6GC maybe a little more (35W max output).

Absolute Max ratings:
6L6 - 22.8 watts
6L6GC - 33 watts
807 - 25 watts

I'm getting a new transformer and some new output transformers. When I get the new gear I want to triode strap the output tubes to see if this will indeed improve the sound.

Cheers,
Bob

Did you already figure out and order the new tranny's, or did you want some help?
 
What kit did you guys buy? I wanna try working on electronics which I really have not done before but maybe you guys could help me.... Its cheap enough if that if I wreck it I wont care
 
Mike ,(Siliconray)
I have been following the 6p3p discussion and it seems that there are alternate parts (upgrade ) available for this kit. Is Bob getting an upgraded OPT? I am certain of the ALPs pot already. So when I am ready for my order can I specify for these upgrades then?
 
Mike ,(Siliconray)
I have been following the 6p3p discussion and it seems that there are alternate parts (upgrade ) available for this kit. Is Bob getting an upgraded OPT? I am certain of the ALPs pot already. So when I am ready for my order can I specify for these upgrades then?

Yes getting an upgraded PT and OPT's.

Cheers,
Bob
 
What kit did you guys buy? I wanna try working on electronics which I really have not done before but maybe you guys could help me.... Its cheap enough if that if I wreck it I wont care

I built the 6P3P se kit from Siliconray check out his store. Just so ya know and a warning, there will be +400V inside this amp. That's enough to kill you. I started building low voltage stuff (preamps) that are even cheaper that this, to get myself used to working with transformers and AC voltages with a long term plan to build a point to point amp just like this one. It's pretty easy but you need to be aware of safe practices, you can not afford to make mistakes. Slip with a probe from your DMM and you will be in for a BIG surprise at the very least. I almost got 450V jolt from one of the caps that I forgot had 450V (d'uh) on it and when I discharged it with a screw driver BANG - screw driver across the room. I got too comfortable with low voltage caps .... and I'm pretty careful. One hand in pocket and thats no kidding after you apply AC the first time. Prior to applying AC you can do whatever in the case, once AC applied, it's one hand only, no exceptions. My suggestion is to look for a thread or 2 around here with safe practices when working with HT (high voltage) this is VERY important. I'm done my rant you've been warned.

Now on to the good'ns. This amp sounds pretty good stock which really is a surprise, to me at least. I would suggest to get the parts list and order upgraded replacement capacitors AND resistors while your amp is in transit. When building use your new replacement caps and stock resistors with intent to replace them in the future. This way if you mess up and burn out something you have a backup without having to wait for new parts. It's pretty hard to mess up the resistors but the caps are easy to wire the wrong way if you are not careful. But again this is a project for those folks that "PAY ATTENTION TO DETAIL". It's not just a resume line of BS either, your life depends on it. This kit is based on a very simple circuit and straight forward to wire and run. The more I look into the circuit design tho, the more complex it gets. There are folks that take a few years getting this type of circuit design tweeked to the point where there is an actual amp built. So you get a short cut to a result here.

This is a good first amp build project. One other thing to note is your speakers and how efficient they are. Just be aware that the output with this amp will be around 5-7W (closer to 5W). If you have a large room or speakers that are hogs for power (Infinity QLS series come to mind), you will need to think about what you want to drive this amp with. That said, it's all good and you will have a source for help right here on AK. When you are satisfied with what you have be sure to think about giving back, put the Karma in side to side. You get it back x10.

Cheers,
Bob

Cheers,
Bob
 
Last edited:
Bob asked for an alps pot and a pair of Optimus output transformer. the OPT is far better than the original one.
Mike ,(Siliconray)
I have been following the 6p3p discussion and it seems that there are alternate parts (upgrade ) available for this kit. Is Bob getting an upgraded OPT? I am certain of the ALPs pot already. So when I am ready for my order can I specify for these upgrades then?
 
Tony, IMHO the tube gears may not be good start point for you. I'd suggest you to build some silicon amplifiers before that. Something like JLH amplifier would be fine. Our VMA2012, VMA2015 or VMA2016 modules are also great for you, very simple diagram, totally adjust free, cheap enough for everyone. Tannar already saw one of the module.
What kit did you guys buy? I wanna try working on electronics which I really have not done before but maybe you guys could help me.... Its cheap enough if that if I wreck it I wont care
 
Here is a modification of the amp for increased safety. It will provide a path to drain the caps after the amp is shut off. Place a resistor across the first capacitor in the power supply after the rectifier.

Here is how to size it:

First find the voltage on the positive terminal of the capacitor. For this example I'm going to use 450 V. Decide how much current you want this resistor to draw. With a power transformer that has a great deal of reserve capacity you might want as much as 10 ma (0.010 amps). With a transformer that is sized right on the edge of its capacity keep the curent draw low, say down at 1 ma (0.001 amps). The trade offs here: The more current you draw the higher the power rating and cost of the resistor, but also the faster the caps are drained (increased safety and less time to discharge before you can work on the device safely).

Since this thread makes it clear that there is not much reserve current capacity in these power transformers I'm going to select the minimum current you should use, 1 ma for this example.

Desired current = 1 ma.
Source Voltage = 450 V.

Divide the voltage by the current:

450V ÷ 0.001 amps = 450,000 ohms​

OK: You need a resistor of 450,000, or 450K ohms.

Now you need to know how much power you expect to dissipate in that resistor.

You already know the current through the resistor, you chose that at the beginning of the design. You also know the voltage of the circuit, 450 Volts. To find the power you multiply the two.

450V x 0.001A = 0.45 Watts​

You always want to oversize your resistors, I like to be at least double the expected power dissipation or more. Anything less is asking for a failure down the road in my opinion.

0.45 W x 2 = .9 Watts.​

Next standard value for a resistor power dissipation is 1 watt.

OK. You now know you need a resistor of about 450K ohms, 1 watt to to make this change. Looking at, say Mouser, you find that they have a selection of 21 different resistors to choose from that range in value of from 430K to 470K, wattage ratings from 1 to 2 watts and prices from $.06 each to $2.21 each. Any one of them would do the job. None of them would affect the sound quality of the amp as it is not part of the signal path.

Shelly_D

Here is the search results of the mouse site:

http://www.mouser.com/Passive-Compo...Z1z0vk1gZ1z0vkjkZ1z0vknvZ1z0z819&Ns=Pricing|0
 
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