• 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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#222
As your tranny is more than capable, it's obviously the tube characteristic that governs this. Note the output is flatter with increasing current if using a choke input (8H), maybe only 5V difference between these two currents. Your local transformer manufacturer may be able to make one up for maybe $20-30.
Click to expand...

Thanks for the tips. I will try a higher value cap first to see how much the B+ rises. If not enough then I will try a choke. I had my tranny's hand built by a local contact.
 
#223
Turn on current

Hi,

I have my aikido preamp with 2200uF PS caps and the PT is rated for 70mA.
When I turn it on, the PT vibrates for 2 seconds until the PS caps are fully charged. The initial inrush current is cca 0.5A. Should I worry about my PT? Should I implement some sofrt of inrush current limiter, or can I live without it?

Thanks.
 
#224
Re: Turn on current

kacernator said:
Hi,

I have my aikido preamp with 2200uF PS caps and the PT is rated for 70mA.
When I turn it on, the PT vibrates for 2 seconds until the PS caps are fully charged. The initial inrush current is cca 0.5A. Should I worry about my PT? Should I implement some sofrt of inrush current limiter, or can I live without it?

Thanks.
Click to expand...
Ouch....presume you have solid state rectification. A choke would slow this inrush down (70 x rated current!!!!). The risk is damaging the winding in the tranny - heat causes delamination, causes vibrations etc etc. All fairly undesirable, especially with high voltages! :bigeyes:

Not sure you need 2200uf - I think I'm only using around 400-500uf in mine...I measure about 4mV P-P noise on my output using an old Tektronics 475 CRO.

Hope that helps.
 
#226
Re: Turn on current

kacernator said:
Hi,

I have my aikido preamp with 2200uF PS caps and the PT is rated for 70mA.
When I turn it on, the PT vibrates for 2 seconds until the PS caps are fully charged. The initial inrush current is cca 0.5A. Should I worry about my PT? Should I implement some sofrt of inrush current limiter, or can I live without it?

Thanks.
Click to expand...


As SS said you must have a Solid State rectifier, otherwise your tube would be TOAST...:dead:
As far as worrying, no, correct the problem and be done with it before you are sorry. A TV diode sounds like the perfect part. Thermistors, you can buy them from Digi-key or Newark. Cheap insurance.
Ron
 

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#227
Yes I have SS rectifier. Thermistor will not help. because it doesnt have enough cold resistance. I need min 300 Ohm to not to go over 70mA when caps are charging.

I am going to do it like this: one mains switch (heaters warm up), one standby switch (anode voltage with inrush resistors in), third switch will bypass inrush resistors.

I could also drop there relays with delay circuit, but it is more complicated.
 
#229
I had to put 2.2k resistor in series with secondary to limit the inrush current to 80mA. So I dont think soft-start on primary will work well.

Low impedance supply and high PS capacity is what I like, thats why 2200uF, it sounds better to me.

I know that manual switches arent the most convenient solution, but if it is going to save my PT, why not.
 
#230
Quote:

It has shown there is a positive effect on the sound quality, compared to adding the power directly. Normally, it takes ½ to 1 hour from turning on the power until an amplifier sounds optimally. With a soft start circuit this warm up time is reduced to a few minutes. Presumably because some of the negative effect on sound quality, that is normally experienced on amplifiers without a soft start circuit comes from the huge start-up current on the capacitors when cold starting the amplifier. This current can be in the reign of 70 - 200 Amperes.

I could be badly mistaken but this sounds like ******** to me. Adding this remarkable soft start is going to make the amplifier sound better quicker?🙂
 
#231
quote:
Originally posted by kacernator
Hi,

I have my aikido preamp with 2200uF PS caps


I don't know but this sounds like way overkill to me. I have built a number of the Aikido line stages and never used this much capacitence in the power supply. Please do tell why this much capacitence would ever be needed? I would think it would make the low end sound somewhat muddy.
 
#232
When I was experimenting with PS of my Aikido I discovered I like low impedance high capacitance supply. The more capacitance I added the more it sounded tighter in bass, more detail, bigger soundstage, better treble, more punchy. So I settled at about 2000uF for one channel.

If you have high impedance supply, the lower capacitance sounds better.
 
#233
Interesting. If one were to buy an aikido amp kit, would it be advisable to buy the psu kit as well? And then swap caps as desired once that's been running? As opposed to building a self-tailored psu from ground up.

I'm looking at the glass-ware kit, this is a good starting point no?
 
#234
Interesting. If one were to buy an aikido amp kit, would it be advisable to buy the psu kit as well? And then swap caps as desired once that's been running? As opposed to building a self-tailored psu from ground up.
Click to expand...

JB sells some nice stuff now. He's always coming up with new kits of very high quality.

I bought Bas's psu board and have had no complaints. Very easy to build with good performance. Maybe Gregg (from Canada) has some for sale on the forum.
 
#235
Olle

Can you tell me a bit about your EL84 amp?

I'm gathering parts together to build my first integrated amp maybe with some EL34, EL84's or KT88. Depends on what I can get hold of on ebay.

Thinking of a simple SE. Maybe with a 6N1P/5687 or 6N6P front end and KT88 power tube. I just got 10 x 6N6PI tubes for 20 USD.I have some 5687's and 6N1P's.
How much gain do I need from the pre-tube to drive the KT88/EL34? Maybe I'll need a 12AX7??

😎
 
#237
Brit01 said:
Olle

Can you tell me a bit about your EL84 amp?

I'm gathering parts together to build my first integrated amp maybe with some EL34, EL84's or KT88. Depends on what I can get hold of on ebay.

Thinking of a simple SE. Maybe with a 6N1P/5687 or 6N6P front end and KT88 power tube. I just got 10 x 6N6PI tubes for 20 USD.I have some 5687's and 6N1P's.
How much gain do I need from the pre-tube to drive the KT88/EL34? Maybe I'll need a 12AX7??

😎
Click to expand...
I know 12ax7's are common on commercial el34/6550 amps, they usually run one per channel, so one 12AX7 for every 2 34's/6550's commonly. But whether the commercial amps are doing it right, or doing it easy, is the real question.
 
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