• 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.

Poll..anyone interested in an Aikido linestage PCB group buy?

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#421
2wo said:
Hi there,
Haveing just figured this out just now...

once you have your pic, save it to your desktop (so you cand find it again) At the bottom of the reply screen there is an 'attach file' section click on the 'browse' button, then find your photo and click on it. that should do it. Like this
Click to expand...


That's what I thought but I can't see the image when I check preview. Here is an attempt to attach a photo:
Steve A
 

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#425
2wo said:
No there is just one primary I double checked the in and out voltages, there is ~250VAC at the output which led to the thought that maybe one of the diodes is bad or not connected properly and it’s half waving but no it’s not . John
Click to expand...


If you check from "in" to "out" you should see 500v for a CT. You should see 250 from CT to either end.

It's unlikely to be the caps. Check the DC voltages at each point after the rectifier. Then start disconnecting components from the output end. This will be easy to diagnose.

Sheldon
 
#426
To SteveA,

Remember when you use psud2, you need to set a reporting delay. I use 30s by default . This lets things settle down to a steady state voltage before reporting.

All in all this looks pretty close, I changed R2 to 2k and got 235V. This is close enough to build. A sim is not nearly perfect. Just see my last post or two. Don’t tear your hair out trying get spot on. This is tubes after all. 10% would be 198-242.

If you are building with the power supply PCB, do not add the diodes. Sim it for yourself and see what happens. (Just a change to a SS full wave bridge is close enough for demo proposes) …John
 
#428
No,
If you do not use a delay you will not get usable info.
What you can do is turn on warnings. This will tell you if you are overdriving your rectifier. On the other hand it will flag if you exceed anything, by even one cycle, so you still need to use your judgment.
If you keep your input cap to a reasonable value and keep an eye on your currents. You should be good to go

Watch out for brain farts, Look above. I was modeling my Aikido supply and forgot that a quirk of psud2, for a full wave rectifier, the transformer voltage you enter is from one leg to the CT not the rated voltage.

SteveA take note of this.

Remember this is a tool not an oracle...John
 
#429
2wo (and anyone else)-
2wo quote:If you are building with the power supply PCB, do not add the diodes. Sim it for yourself and see what happens. (Just a change to a SS full wave bridge is close enough for demo proposes) …John

Do you mean don't include the diodes in the PSU sim or leave the diodes off the pcb (if off the pcb I don't understand). I used a 5 sec delay in my simulations.

The PSUD info Bas posted on page 21, was that intended to be the simulation corresponding to the PSU V1.0 from page 27 (I don't follow the 450R)? I am trying to understand C-R-C-R-C in terms of the components listed on the V1.0 schematic.

When I simulate (editing the PSUD simulation from page 21) using C1=1uF, R1=1k, C2=180uF=C3, R2=2k) I get 226V without getting the message: IFRM exceeded........ BTW, I would assume one should simulate to avoid this condition.


Thanks,
Steve
 
#430
Hi Steve,
I am sorry I have given you bad information.

The supply you copied above, is a full wave. One diode or tube section, on either end of a center taped transformer, with the center tap as ground.

To model this in psud2, with a 250VCT (125-0-125 ) transformer you use 125 as your transformer voltage.

Bas’s supply is a hybrid full wave bridge . 2 tube sections and 2 diodes.

There isn’t one in psud2 so you model your supply with a tube bridge, then change it to SS bridge.
Your voltage will be somewhere in the middle. The difference is not huge and will give you an idea.

However this time we take the same 250VCT transformer, ignore the center tap and use 250 as the transformer voltage.
 
#431
floating heaters

hi guys

i've read thru this thread a few times and still am a little unsure about floating heaters.

Aikido_Amplifier.png


from the above schematic, cathode top section of first tube and cathode bottom section of first tube will operate at vastly different voltage.

if this is physically one tube, how do i float the cathode of the top section if the tube has a common heater?

thanks.
 
#432
if this is physically one tube, how do i float the cathode of the top section if the tube has a common heater?


The answer you can’t .as you raise one half the other goes for the ride. This won’t do any harm, some say it’s a good thing. Just watch that you don’t bias up so high that you exceed the V hc for the lower half.

Another thing if you are using two identical tubes you can use one for the top and one for the bottom. And just bias the top. This really limits tube rolling though.

This brings another point. A 6sn7 has a V hc of +/- 200V. Most of the nine pin types that we are using are +/- 100V.

The 300k/100k divider gives me ~74V at 220V B+ and my highest cathode voltage is ~118V and lowest is ~ 1.5. So I am good to go.

But something to consider if using a different B+…John
 
#433
2wo said:

The answer you can’t .as you raise one half the other goes for the ride. This won’t do any harm, some say it’s a good thing. Just watch that you don’t bias up so high that you exceed the V hc for the lower half.

Another thing if you are using two identical tubes you can use one for the top and one for the bottom. And just bias the top. This really limits tube rolling though.

This brings another point. A 6sn7 has a V hc of +/- 200V. Most of the nine pin types that we are using are +/- 100V.
Click to expand...

thanks for the reply john.

i am under the impression that it cannot be done as well.

i've considered using same tube types so that both sections of one tube can be used for top and another tube for bottom. that way, i can raise the heater supplies for each tube correctly.

like you mentioned, it really limits the tube rolling... which brings the question of whether it is worth it to raise the heaters to the table.
 
#436
2wo said:
Hi there I dont want to give the wrong impression.
Click to expand...
no worries, none given. 😉

Sheldon said:
Just make sure you are within the limits. The designer didn't worry about it.
Click to expand...
sure, will check for that.

i'm just thinking of using some tubes that i have on hand, rather than go all out to procure other tubes for this project. i have some 6072, 12AU7, 5687 and 6SL7 that might be suitable.

was thinking of using 6072 + 6SL7 (5687 is too current hungry on the heaters).
 
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