• 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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Max Martin

Max Martin

Member
Joined 2011
Ok this is what i got today,

Over dropping res: 13,35V

B+ 195V
Cathode 0,75

This was with dropping res 2x2,2K parallel (1,1K) and cath res 150ohm. Didn't have time to try anything else.

It sounds nice now. Best yet i think, but hum is quite strong in bass. When i turn my bass amp off it almost stops. It seems that the other hizz again is little lower but still "there". Easy to hear in the evening when all traffic outside my windows is gone.
 
Max Martin

Max Martin

Member
Joined 2011
how it looks now in the PSU
 

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C

cjkpkg

Member
Joined 2008
Yes everything looks OK, you are dropping about 12mA at the dropping resistor and 5mA at each tube so 2mA in other losses through the circuit.

Putting the MKP in front of the choke can help with hum/buzz.

Also I would put the cathode resistors back to 180 and see if that helps the hisss.
 
Max Martin

Max Martin

Member
Joined 2011
Another thing, you saw how i have my "layout" in the pics. Do you think a new install also will help with this hum? I mean transformer/choke under a cover. All cabling nice n neat and so on... I mean it can't be worse right. I actually have an shielded cable i'm gonna use only for heaters. Now i have signalcable hehe;) also shielded.
 
Max Martin

Max Martin

Member
Joined 2011
Wow, many questions and here is one more.

To fuse this i have first on the back (230v inlet) 3A and on one secondary before rectifier there is one 0,5A to protect my transformer if rectifier blows. Is this ok? Don't really know how to calculate total current/ or how big fuse(s) i need.

Thx
 
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cjkpkg

Member
Joined 2008
3a seems a little high. think about the VA rating of the xformer total...that is watts. Watts/volts=amps. if you have a VA rating of 50 then divide by your mains voltage 50\220=.23A. I would use no more than .5A.

Here in the states we only have one hot and one neutral for the AC mains. Until recently Earth was optional, most newer homes have 3 prong outlets though.

Typically here you would only fuse the hot. If you have two hots and an earth and only one is fused and it blows you will still have 110v on one leg terminating somewhere which is dangerous.

Someone more versed in typical EU safety fuse layout should chime in.
 
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cjkpkg

Member
Joined 2008
Just remember if both legs are hot and only one is fused and it blows and the mains is still hot the other leg will still be hot.

With a catastrophic failure you really want the whole xformer to power down.

At your outlet in your house is it a 2 prong or 3 prong outlet? I am not familiar with mains wiring in Europe. One hot 220 one neutral one earth? Or two hot 110 etc...

It is important to know the entire circuitry so that your fuse does what you want it to....cut all power to the amp not just half.
 
Max Martin

Max Martin

Member
Joined 2011
It's

Phase
Neutral "0"
Earth

in here,

but in my house (older. built 1972) there is no earth only phase/neutral. Usually when they do some kind of renovation then the electrician put new sockets with an earth and (also totally new wiring) and also childproof with covered holes. In Sweden (where i came from, there are far ahead with this)

I almost got choked when i came over here 5 yrs ago and saw they still have this. Only in my childhood (i'm born -79) i saw this type of outlets without earth and childproof holes. A lot change in Sweden in the 90's. Over here it's still the 80's :D

I'm myself a construction worker (bricklayer) and sometimes i talk little to the electricians about this things.
 
Max Martin

Max Martin

Member
Joined 2011
Ok NOW something happened!

Because of very little time today i only put that MKP before choke and

262V

cathode 1.2V = 8mA? right?

I listen couple of minutes before i knew about this (measuring) and it sounded really good and i thought to myself.. this is it =) Pretty high voltage though ;)

MKP is 2x2,2uF WIMA MKP4

Tomorrow i have to put higher cathode res again for sure.... and probably dropping res too? Hum and buzz was pretty ok now. (in daytime atleast)
 
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Max Martin

Max Martin

Member
Joined 2011
cjkpkg said:
3a seems a little high. think about the VA rating of the xformer total...that is watts. Watts/volts=amps. if you have a VA rating of 50 then divide by your mains voltage 50\220=.23A. I would use no more than .5A.

Here in the states we only have one hot and one neutral for the AC mains. Until recently Earth was optional, most newer homes have 3 prong outlets though.

Typically here you would only fuse the hot. If you have two hots and an earth and only one is fused and it blows you will still have 110v on one leg terminating somewhere which is dangerous.

Someone more versed in typical EU safety fuse layout should chime in.
Click to expand...

So 30/230= 0,13A fuse

Both before xformer and on sec? And is one enough before tube rectifier?

I was thinking my total Ampere. 1,5A+0,5A+40mA is 2A something i was thinking..
 
Max Martin

Max Martin

Member
Joined 2011
Ok some soldering took place today.

With droppingres to 5,1K i got 232V. =ok?

and with cathode res (all 4 ofcourse) i got about 5mA per tube (or 1,2V)

Hum is "ok" and buzz is almost gone. It's sounds distorsionfree, open, clean, musical, involving, really good bass, tight clean and DEEP. Altogheter smooth and pleasant. I think rather coupling cap set the standard here?
Should i settle here or??
 
popilin

popilin

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Joined 2010
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