• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Building a Aikido preamplifier

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#301
What I think SY is saying: he likes us to figure things out and not just spoon feed us.
Click to expand...

LOL. I do a lot of spoon feeding at work. Though it was about time someone spoon feeds me!

Besides that its 9.30 pm here and still about 34 degrees C with smoke shrouding the house as we have forest fires blazing away around our town:bigeyes: :bigeyes: :bigeyes:

I need a nice cool Rum and Coke.
 
#302
Brit01 said:
Hi Ron,

Thks for the link.

In the table he suggests 89,474 for the R15 if I'm using the 6N1P. Does it matter if I'm using the 5687 as output tubes?

I guess as you suggested to use a pot and see if there is any difference as I change the value.
Click to expand...

Hey Brit

If you look at the schematic, the first valve (your 6n1p) will not be affected by choice of R15. You should be looking up the values to suit the 5687 and the B+ you are planning to use.
 
#304
Here's what I mean. Suppose the two series values are 20k and 60k (just making these up) and you take the noise signal off of their junction. Instead use a 15k, a 10k trimmer, and a 56k in series, taking the noise signal off of the wiper.

Alternately, use a 30k and a 60k, then parallel the 30k with a series pair of a 100k resistor and a 100k trimmer with its wiper connected to one end. Sorry, I'm not at my computer with the schematic drawing program...
 
#308
You'll have a gain of about 15 with that circuit. That will take your 2V source to 30V at full throttle. I suspect your amp is not going to need that level of signal, but that is a very uninformed opinion. I've built several with that gain structure along the way...
Click to expand...

I changed R15 from 80.6K to 78.7K (supplied by JB) but no difference.

I'm currently testing the board with a laptop for the source and a pair of active pc speakers as the load.

Now I'm thinking about the quote above. Maybe this is the issue here. If I turn up the volume with the music paused, I hear the buzzing.

Maybe it is just too much current going through. In fact I have a gain of about 30-35 with the 6N1P's:bigeyes: :bigeyes:

Could this be the issue? Just amplifying every little tiny bit of noise.
 
#310
Well I found some 12B4 tubes at 5 USD each from Radio Electric supply. I might try these with a much lower mu of 6. So half of this and through the 5687 I should get about 2.80 gain.
This may work better with my SS amp in the meantime.

I have a question regarding Bas's psu. if I was to experiment with different size of caps would it be C2, C3 or C4 I adjust?
(Currently C2/3 = 100uF and C4 = 47uF).

Which would have a greater impact on the performance?
 
#313
Brit01:

Adjusting the caps in Bas' PSU board will change the B+ voltage and ripple. Use PSUDII software to model your changes, since the C, L, R values are somewhat inter-related.

Are you using a choke in the PSU or a resistor?

If you are running a 6N1P as the input tube, your gain should be half of the mu of the tube, or roughly 36/2=18

It looks like you could run a 6H30 for 15/2=7.5, or a 6CG7 for 21/2=10.5

JB's Aikido tube table gives several operating conditions for each input tube (basically cathode current and B+ voltage). So look at the entries for low mu tubes, and get your B+ voltage, R15 and R16 close to the table values, and you should be good to go with a newly selected input tube.
 
#314
Adjusting the caps in Bas' PSU board will change the B+ voltage and ripple. Use PSUDII software to model your changes, since the C, L, R values are somewhat inter-related.
Click to expand...

thks boywonder.

I was playing around with the C1 cap last night trying to increase the B+😀
Didn't have enough microfarads on hand. Have to buy stuff on ebay.
My local shop told me that non polarized caps more than 4uF didn't exist!!!Welcome to Uruguay!

Using about 6.5 uF so far with a B+ of 238. I want it at 250V. Have to increase this just a little more.

What would you hear when ripple is present? Or just on the scope?



Are you using a choke in the PSU or a resistor?
Click to expand...
resistor here



So look at the entries for low mu tubes, and get your B+ voltage, R15 and R16 close to the table values, and you should be good to go with a newly selected input tube.
Click to expand...

I installed a trimmer last night and was adjsuting R15. There really wasn't much variation. I've got it set at 80.6K for the 6N1P/5687 combination.

I have some 6N6P's in the post (they have a fairly low mu). They were good value. Also looking for some 12AU7's. Got some 12AX7's coming also for future projects😀 😀
 
#315
Have you played around with PSUDII? If you are using a 6X5 rectifier tube (which I am assuming that you are, since you are using Bas' Board), you need to be careful with the value of the first cap because you can easily exceed the max forward current of the tube rectifier.

SS rectifiers allow a lot more leeway for the first cap choice, as they are not as sensitive to max forward current as tubes are. If you really need to bump up the B+, you could whip up a SS rectifier, this would drop approx 20 less volts than the 6x5 tube also allowing a higher B+. If you do this, you will still need the voltage divider for the heater bias.

Just for giggles, I pulled up the PSUDII simulation for my aikido supply, and with a 4 or 5 uf first cap I am exceeding the forward current of the 6X5 by about 3X, so you may be pushing your luck already with the 6X5. I am running a CLC with a .22 uf, 30H, 220uf. The 30H choke is in place of R1, making it a CLC instead of a CRC. R2 and R3 and 220 ohms, and my transformer is 250V, so YMMV. IIRC, my B+ is around 220V or so.

I am unfamiliar with the 5687 Aikido board, but if you plan on mixing 6v and 12v heaters (as in 12AU7) you'll need to change some jumpers on the board. It appears that the 5687 can be wired as 6V or 12V so you should be all set even if you need to run all the heaters at 12V.

Use PSUDII to model your PS to minimize ripple; you want as a clean of a DC signal for B+ as you can reasonably get, to minimize noise.
 
#316
BW,
30H choke ! Holly Cow that seems huge. Wouldn't that large of a L spike the voltage at startup?
I'm running an 8H on Mr. Bas' 6x5 PS board. C1 is .66uF, my transformer is slightly oversized which helps keep my first cap Very small. Transformer V is 300. B+ Voltage is steady at 297.
Close enough to my target 300V.
Ron
 
#317
I tried to load PSUDII on XP but it just wouldn't load the exe. I'll try again to tonight.

Have you got the link handy?

I'd like to try SS rectification. I will research into that. I'm here to learn and tweak as much as possible.

My tranny is 275 V. Maybe I should have gone for a 300.

Yep got the jumpers figured out for the 6/12V tubes ok. It's pretty straight forward on his latest boards.

I might just bump the first Cap down a little to avoid damage to the 6X5. I did read somewhere it can take up to 16uF but this depends on the brand I believe. I have a Hytron and National Union NOS.


Just tried it through my power amp with the line level way down and no hum at all. Very silent. Only when I turn up the line level on the power amp with the music paused I hear the hiss. Probably due to the high gain and sensitive Klipsch.
 
#318
Renron said:
BW,
30H choke ! Holly Cow that seems huge. Wouldn't that large of a L spike the voltage at startup?
I'm running an 8H on Mr. Bas' 6x5 PS board. C1 is .66uF, my transformer is slightly oversized which helps keep my first cap Very small. Transformer V is 300. B+ Voltage is steady at 297.
Close enough to my target 300V.
Ron
Click to expand...

PSUDII shows a nice smooth voltage rise with no overshoot. I have access to a scope but so far, I am a complete knucklehead when it comes to operating it. This will be another great exercise for my scope education.
 
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