European build

[cedricb]

At last I've received everything for my European build...

I've made a sketch for the top of the case:
- wooden frame of 330mm x 280mm (which I think is the standard in HiFi)
- the yellow line delimits the aluminium plate
- the blue line delimits the inner section of the wood
- the 3 big circles are the transformers from Trafomatic



The output transformers have a diameter of 90mm and the power transformer has a diameter of 140mm (don't know why is so big).

It looks like Mickey Mouse...

[cedricb]

On the power transformer, there are 2x6.3V. How do I find out which wires are supposed to be in parallel ? I've got 2 pairs of red wires...

For the output transformers, how do I find out which pair to use for the "plate" and "screen" ?

[DeathRex]

On the power transformer, there are 2x6.3V. How do I find out which wires are supposed to be in parallel ? I've got 2 pairs of red wires...

You can use a multimeter to find the 2 wires for one of the 6.3 volt seondaries. Should measure <1Ohm.

Should be red, yellow, or white = B+
Green or blue = filament

[cedricb]

On the power transformer, there are 2x6.3V. How do I find out which wires are supposed to be in parallel ? I've got 2 pairs of red wires...

You can use a multimeter to find the 2 wires for one of the 6.3 volt seondaries. Should measure <1Ohm.

I've got the 2 pairs that's fine. But I was wondering on J1 - pin 7 and 8; you need to parallel the 2 pairs to provide 5A. For example for the PA-774: you need to use the brown with the green and the brown/white with the green/white.
My problem is; my 2 pairs of wires are all red...

[Ty_Bower]

I guess if you get them backwards, the two 6.3 volt windings will be out of phase and you'll net 0 volts. I'd think you would also short the windings this way, draw a LOT of current, and probably ruin the transformer.

If you had a dual trace scope, you could watch the phase of both windings at once and figure out pretty easily how to wire them in phase with each other. I guess you could also wire a 1 amp fuse in series with one of the windings, and then try it. If the fuse blows, you did it backwards.

Aha! Here's your answer:

Color coding should do it providing the manufactuer did their job correctly. Without any testing, you have a 50% chance of getting it right the first time. Put a 60 watt lamp in the primary to be safe on the first power up. (unloaded) If it's right, the lamp won't light.

[dcgillespie]

An easy and safe way to determine the phase of otherwise identical low voltage windings is to wire them in series, and then measure the voltage across the remaining two leads. If it is nearly 0, then they are wired buck style. If you get double one of the winding's voltage, then they are wired series aiding.

When they are wiring in series aiding, the wire from one winding at the series connection is of the same phase as the wire from the other winding that is connected to the meter.

When wire color has faded into nothing, this makes for an easy way to determine phase quite easily.

Dave

[cedricb]

DOH!! I should think a little bit more... I'll wire the secondaries in series; if I'm getting 12.6V then it's out of phase for parallel...

[cedricb]

Hi,

Here are my measures...

V1: RAYTHEON 5751 Windmill Getter 1960's
1= 100.8V
2= 2.7mV
3= 929mV
4= 3.060VAC
5= 3.071VAC
6= 102.8V
7= 3.4mV
8= 919mV
9= 3.057VAC

V2: RCA 12BH7A 1960's
1= 241V
2= 100.5V
3= 108.4V
4= 3.070VAC
5= 3.070VAC
6= 239V
7= 102.8V
8= 110V
9= 3.065VAC

V3: Russian EL84M 1976
2= 38mV
3= 15.45V
4= 3.065VAC
5= 3.043VAC
7= 383V
9= 385.6V

V4: Russian EL84M 1976
2= 35mV
3= 13.93V
4= 3.044VAC
5= 3.095VAC
7= 382.4V
9= 385.4V

V5: Russian EL84M 1976
2= 21mV
3= 14.89V
4= 3.096VAC
5= 3.090VAC
7= 382.7V
9= 385.7V

V6: Russian EL84M 1976
2= 25mV
3= 15V
4= 3.117VAC
5= 3.119VAC
7= 383V
9= 385.5V

J1:
1= 312VAC
2= 312.5VAC
3= 26.35VAC
4= 26.36VAC
7= 3.183VAC
8= 3.187VAC
9= 346VAC
10= 345.7VAC

Last night; I've biased V4 / V5 / V6 to ~350mV after 1/2h. With V3 I couldn't go bellow ~370mV. The pin 9 were at 400V last night.
This morning, the bias for V4 / V5 / V6 were ~330mV after 10min; so I've re-biased to ~350mV. For V3, I can't bias above ~340mV and it doesn't make any different how much I turn R22; the voltage stay the same...

So far I've used 2 power resistors of 8.2 ohms 25W for the load and I've shorted the inputs with 2 wires.

How long do I need to wait until biasing and getting a good reading? What do I need to do with V3 ? ...change it?

On the power transformer, I've got two taps for 230V and 240V (if the main is high). At the moment I'm using the 230V tap.

To burn in the power tubes, can I leave the inputs with shorting wires or do I need to use a proper input source? ...any preference for the type of music? ...metal / blue / pop-rock ?

So far the amp has been powered only for 1h because I couldn't get a proper voltage reading for the bias and the voltages are a bit different than the manual.

Please let me know what do I need to do...

[cedricb]

How long do I need to wait until biasing and getting a good reading? What do I need to do with V3 ? ...change it?

I've replaced tube on V3 and I can bias it normally...

Do I need to worry about the 383V and 385V on the power tubes? ...and about the additional 40V for the tube on V2 ?

Otherwise I've being listening different type of music and here are my finding:
- the music was really boomy at first, the speaker were vibrating... how long do I need to break in on these tubes?
- I think I'm getting more power on the right speaker than the left one, how can I verify it via my multimeter? (just to be sure it's not my old speaker or my ears or the recording)

For the time been I've using an old portable CD player (Technics SL-XP170) and speakers 90 dB/w (from a JVC MX-D302T).

Ray Charles is still a little bit boomy; is it something wrong with the board/soldering or my speakers are not up to the job?

Otherwise the output transformers are dead cold and the power transformer barely warm!

Otherwise any comments on the top plate? Do you think I need to have a circle of holes around each tube?

[cedricb]

The power transformer is warm due to extensive heating from the power tubes on the back...

[TomMcNally]

I've replaced tube on V3 and I can bias it normally... *** good deal

Do I need to worry about the 383V and 385V on the power tubes? ...and about the additional 40V for the tube on V2 ? *** don't worry about either

Otherwise I've being listening different type of music and here are my finding:

- the music was really boomy at first, the speaker were vibrating... how long do I need to break in on these tubes? *** The amp is capable of reproducing whatever you put into it, with great bass ... don't worry about break in time ... I think it's mostly a myth

- I think I'm getting more power on the right speaker than the left one, how can I verify it via my multimeter? (just to be sure it's not my old speaker or my ears or the recording) *** put a meter across it on an AC scale and measure it with steady state tone ... 400 Hz or 1000 Hz is usually used for quick checks ...

For the time been I've using an old portable CD player (Technics SL-XP170) and speakers 90 dB/w (from a JVC MX-D302T).

Ray Charles is still a little bit boomy; is it something wrong with the board/soldering or my speakers are not up to the job? *** you can't use one recording as a standard

Otherwise the output transformers are dead cold and the power transformer barely warm! *** great

Otherwise any comments on the top plate? Do you think I need to have a circle of holes around each tube?

*** looks good, you don't need any more holes, the gap around the tubes will vent the small amoun of heat from the resistors on the board

Nice job - box it up and enjoy the music !

[20to20]

Do I need to worry about the 383V and 385V on the power tubes? ...and about the additional 40V for the tube on V2 ?

You'd have to have faith your tubes could meet 7189 type quality.

[EWBrown]

I found, a couple years ago, that the Trafomatic ST35 power transformers do run higher B+ voltages than normal for EL84s. In my case, I had approximately 400VDC at the OPT centertaps, which is 35VDC higher than normal ST35 operation (365VDC) The Russian made EL84s / 6P14Ps are inexpensive and easily available enough so that shortened tube life isn't really as much of a problem as it would be with choice Telefunkens, Mullards, NOS USA 6BQ5s, etc.

There are two simple solutions, first is to use a 10 to 12 VAC 2A (or greater) transformer to "buck" the incoming (230-340 Volt) AC power line voltage by approximately 5%, and the other is to bias the tubes slightly lower than 35 mA, try 32 to 33 mA (320 to 33o mV) , this should lower the plate dissipation sufficeintly, and not affect the sound quality.

As far as the "boomy" bass, are you using a preamplifier with tone and loudness controls? (In the photo, it looks like you have direct conenction from the CD player to the ST35 amp)

If you are, try setting them to the "neutral" center position, and turning off the "loudness" contour switrch if there is one. If you are using the "headphone" output of teh CD player, rather than the "line" output, it may have bass boost and somewhat "flabby" sound, as this is intended to work into a 32 to 300 ohm impedance. The line output should be a lot "cleaner" sounding.

In my systems, I use only volume controls, and "balance" in a couple of builds. No tone controls, loudness, equalizers, etc to modify or mangle the sound.

The chassis holes around the tube sockets are more than sufficient for vertical air circulation around the tubes, no need for any more drilled holes.

/ed B

[cedricb]

That looks like it is at the high end for plate voltage compared to 6BQ5's. With your bias at 15v I believe you are near cutoff and be will close to running in Class B. Was that your intention? Someone correct me if I'm wrong, please.

I don't want to do anything fancy...

I found, a couple years ago, that the Trafomatic ST35 power transformers do run higher B+ voltages than normal for EL84s. In my case, I had approximately 400VDC at the OPT centertaps, which is 35VDC higher than normal ST35 operation (365VDC) The Russian made EL84s / 6P14Ps are inexpensive and easily available enough so that shortened tube life isn't really as much of a problem as it would be with choice Telefunkens, Mullards, NOS USA 6BQ5s, etc.

There are two simple solutions, first is to use a 10 to 12 VAC 2A (or greater) transformer to "buck" the incoming (230-340 Volt) AC power line voltage by approximately 5%, and the other is to bias the tubes slightly lower than 35 mA, try 32 to 33 mA (320 to 33o mV) , this should lower the plate dissipation sufficeintly, and not affect the sound quality.

Another thing, I've got a 240V tap on the power transformer; this should lower everything on the secondary.

As far as the "boomy" bass, are you using a preamplifier with tone and loudness controls? (In the photo, it looks like you have direct conenction from the CD player to the ST35 amp)

If you are, try setting them to the "neutral" center position, and turning off the "loudness" contour switrch if there is one. If you are using the "headphone" output of teh CD player, rather than the "line" output, it may have bass boost and somewhat "flabby" sound, as this is intended to work into a 32 to 300 ohm impedance. The line output should be a lot "cleaner" sounding.

I'm using directly the headphone output (no preamp), I didn't use the line output because I don't have a volume control yet.

Thanks a lot for the comprehensive comments!

[cedricb]

Another thing, I've got a 240V tap on the power transformer; this should lower everything on the secondary.

J1:
1 & 2 --> 300VAC
7 & 8 --> 3VAC

The 240V tap produced obviously a lower centre tap secondary (300V), but I've got 6V instead of 6.3V.

I've tested the following on V3:
3 --> 13,87V
4 --> 2.932VAC
5 --> 2.911VAC
7 --> 365.6V
9 --> 369V

Any comments please?

Or can I use a resistor on the centre tap output to lower the voltage around 20V? (with the 230V primary tap)