• 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.

My first preamp with tubes

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#382
#383
Been going through every component, measuring caps and so on. Don't find anything wrong... 😕

I have not touch anything for a few days and it have been playing music well... I was thinking can it be that the transformer running on it's edge and today when i cooked it little extra (maybe 5 hours straight on?) it just melted?

I wonder can a tube rectifier go bad, internally, like a short or something? Clearly it seems like even though i switched to 6z4, the problem was still there.

One thing i forgot to mention was that second time i switched it on, transformer made a lot of noise like hum, like "tried" and then came smell.
 
#385
What you'll think of this?

inMADout verkkomuuntaja TA84M36 - inMADout verkkomuuntajat - Verkkomuuntajat - Muuntajat ja kuristimet - Elektroniikan komponentit

One "normal" 6.3v for rectifier and one 3.15-0-3.15 to 6n3p.

Price is much better then hammond. Sec.voltage is quite high (use bigger drop res? Problem solved so i can surf around 280v B+? Something i missed?

Here is some data for rectifier i'm gonna use.

http://rutubes.com/product/6c5s-6x5gt-ez35-tube/

If everything seems ok by you guys i click on the order button.
 
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#387
I guess that folks here think it's a good pt?! Not any negative comments..

What i can see it's overdimensioned for my needs (155VA) but price is ok and so is looks. Screened too, saving 35 bucks on that 🙂

I have placed an order for 4pcs diodes mentioned above. Thx for the tip, jersey😉

I have tearded down my build and looking forward to build up my final coming week or next. Let's see how it goes.
 
#388
I've tried to do new simulations in duncan but I get error message all time saying I'm exceding 0,24mA with 0,34 and so on if i don't use very small caps after choke.

BUT everytime i switch rectifier to 5u4-g all problems seems to be solved. Is it possible to change to 5u4-g?? This new pt have also a 5v /3A filament supply.. Could it be possible? I like big coke bottles hehe😉
 
#389
I was wrong, a soft start tube like 5v4-g is probably better if i like "st" shape. Also it doesn't draw as much current. I thought this new pt could give 3A but again i was wrong. 2.5A is correct and as 5v4 is around 2A it should be ok.

Last night i was doing alot of reading about tube rectifiers.

I will probably get a 5V4-G sylvania nos or something🙂
 
#390
Until you find the cause of failure, keep out tube rolling.

Most probably you have a leaky capacitor, and wouldn't be the first time.
When you exceed max allowed voltage, caps degrades to an extent that are almost a short circuit.

BTW, be in mind that more AC voltage on the transformer secondary, will put higher voltage on caps.
 
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#391
popilin said:
Until you find the cause of failure, keep out tube rolling.

Most probably you have a leaky capacitor, and wouldn't be the first time.
When you exceed max allowed voltage, caps degrades to an extent that are almost a short circuit.

BTW, be in mind that more AC voltage on the transformer secondary, will put higher voltage on caps.
Click to expand...

I have some 400V/450V caps coming in next week. Also MKPs with high voltage) Also my BC caps i ordered from Germany got lost in post but new are on the way.

I suspected that it could be these "old" mkps 250V that was the cause. I measured them and all had exact same value as before (i wrote it down on the side before using them) but i heard something that a cap can be faulty but still show correct value. Anyway, i don't trust them so i use them for crossover in some speakers instead.

Only thing i found could been a problem that one 6,3V wire underneath the board soldered directly to the pin 1 was loose ( had 2 wires twisted for each and one of these was loose i discovered today) so it could be that it was touching ground (very close) or something else and that could be an extra current draw maybe?

I ordered the new PT today and yes tuberolling comes later, i just have to use my 6x5GT for now.

I pray to god that everything goes alright when i'm gonna build up everything from scratch again. I will double check all and also compare to both pcb and schematic when all is soldered. Hardwired it is 😉

So i have a lot of work in front of me this week with this project 🙂 WHen i'm done i probably take a pic and show here before i push the power button, just in case 😀😀
 
#392
popilin said:
Until you find the cause of failure, keep out tube rolling.

Most probably you have a leaky capacitor, and wouldn't be the first time.
When you exceed max allowed voltage, caps degrades to an extent that are almost a short circuit.

BTW, be in mind that more AC voltage on the transformer secondary, will put higher voltage on caps.
Click to expand...

I will try to sim more in duncan and try to come in around 280V DC B+. What i understood higher voltage in this construction is just beneficial. Little hard to know what cathode res should be now. 330R is little to high. 4,7mA for res and 5.3mA for LED last time i checked.Also voltage goes up here i guess.
 
#393
Max Martin said:
I will try to sim more in duncan and try to come in around 280V DC B+. What i understood higher voltage in this construction is just beneficial.
Click to expand...

Higher voltage is beneficial to your SRPP, but be careful to not exceed cap voltage ratings in PSU.

Max Martin said:
Little hard to know what cathode res should be now. 330R is little to high. 4,7mA for res and 5.3mA for LED last time i checked.Also voltage goes up here i guess.
Click to expand...

In SRPP topology, cathode current is about the same for both triodes, so the same current trough cathode resistor and LED, just measure voltage drop.
 
#394
popilin said:
Higher voltage is beneficial to your SRPP, but be careful to not exceed cap voltage ratings in PSU.



In SRPP topology, cathode current is about the same for both triodes, so the same current trough cathode resistor and LED, just measure voltage drop.
Click to expand...

Ok. I think over resistor it was 1,6V and over LED about 1,85V. Little different on the other tube. Should be about 0,4V difference but with leds it was more. Don't remember exactly nrs..
 
#398
I got my "inMADout" transformer today. Weights in on 2,7kg...(5,95 ib) Looks well made (but i also said that about previous..😀) Made in Italy.

One thing that strikes me is that only one sidecover have plasticwashers and other side doesn't? I heard/read something that you can saturate the transformer if cover have contact with the screws/bolts. Maybe somebody understand better what they thought/how it's working?

As ususal i have problems to upload more than one pic at a time so one by one...
 

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