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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 14th August 2016, 04:08 PM   #1
hhibrownsbacker is offline hhibrownsbacker  United States
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Default SSE sounds good BUT???

Alright I fired this up yesterday and ran it thru some of Ty_Bowers suggested tests. It sounds good with no distorting or anything else. I'm just trying to fine tune it. Its set up in Ultralinear with feedback.
First question I have is on the Diodes supplying the rectifier tube with High voltage. With them in circuit I only get readings of 166 V at pin 4 and 6. If I bridge the diode I get readings of 408V which is more in line with what he says you should expect. Do I need to leave these or pull them.
Second question is about adjusting the cathode voltages. I believe if I read this correctly this is dependent on several factors like power tranny(Hammond 274BX), 5000K outputs, Tubes(KT88), B+ 441VDC, voltages at cathode (41.8 and 42.1), cathode resistors installed are what is suggested in assembly manual (560) with cathode resistance readings (556.4 and 555.3). How do I decide what to change, OR if I need to change any thing at all
Thanks for any and all help,

Last edited by hhibrownsbacker; 15th August 2016 at 08:52 PM.
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Old 15th August 2016, 06:20 PM   #2
wdecho is offline wdecho  United States
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Not sure on the diodes you are talking about. With tube rectification you do not need the Freds diodes. If it is diodes George has added to the board I did not use them on my build being that I built point to point from the schematic but a friend of mine just built the SSE with the board and just put a jumper there but he is using a GZ34 tube. To answer the second question, George has a chart for one to choose the best cathode resistor for the way you have built it. It just so happens that I changed out my cathode resistors this morning from 560 ohm to 400 ohm with 420V to plate and 5000K OPT's using EL34 tubes. It did seem to improve the soundstage. Study the chart and it will start making sense to you.

Tubes and Applications | Tubelab
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Old 15th August 2016, 08:50 PM   #3
hhibrownsbacker is offline hhibrownsbacker  United States
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Thanks wdecho, after starting this thread I read a few have had the same problem with the diodes George added to the board to try to save some of the generic foreign rectifiers. I am using a Amperex GZ34 so Im just going to pull them and install jumpers as they shouldnt be needed. Now as far as the chart George supplied, I dont have a clue what the headings across the top are so its a guessing game for me. Ive studied that chart and although a few of them are pretty obvious, the others aren't so obvious(at least for a novice like me). Im going to replace the diodes with jumpers, take new readings and see if every thing stays the same.
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Old 16th August 2016, 03:38 PM   #4
spendorite is offline spendorite  Canada
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Quote:
Originally Posted by hhibrownsbacker View Post
Ive studied that chart and although a few of them are pretty obvious, the others aren't so obvious(at least for a novice like me). Im going to replace the diodes with jumpers, take new readings and see if every thing stays the same.
In this thread , Simple SE build costs , you will find an explanation for the figures in the table.
The following is what Rknize posted in that thread...........

"They are all rough approximations. Actual results depend on your actual B+, the actual drop through the OPT, the behavior of the tube, etc.

B+ voltage = your actual B+ rail
Load Z = the primary impedance of the OPT
Vp = output tube plate voltage (B+ - OPT drop)
Vk = output tube cathode voltage
Rk = cathode resistor value (R17,R27)
Ik = cathode current
Diss (idle) = output tube plate dissipation at idle (no sound)
Pwr Out = maximum power output
Dist - 2nd = second harmonic distortion
Dist 3rd = 3rd harmonic
DF = dampening factor (how well the output can cope with varying speaker impedance)

The orange "Diss" number are approaching the maximum spec for that tube type. You can see how the harmonic distortion values tend to go down as the tube current (and therefore plate dissipation) values go up. You are trading tube life for improved sound. The red values are "overloading" the tube. This is all based on the old, published specs. Some tubes can handle more without hurting the tube (plate glow) and some can't even meet those specs. It depends on which tubes you choose. Some have better reputations than others.

The point of the table is to give you a rough idea of the trade offs involved when you choose what tubes to run and what OPT primary impedance to get. You'll notice that for a given B+ and tube type, you get more output power with a 3k primary impedance than with a 5k but the trade off is more distortion and lower dampening factor. That choice would be driven more by your choice in speakers. If they are not very efficient (need more power) and but are not too difficult to drive (can live with lower dampening factor), you may prefer a 3k primary and use KT88s. If they are very efficient (95dB or higher), then you will probably get better results with a 5k primary, which lets you run EL34s.
It's all about trade-offs. "


I have the diodes D3 and D4 plus the thermistor TR1 in both of my SSE builds and don't have a problem with them. Both of my SSE's work fine and sound excellent.
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Old 16th August 2016, 04:49 PM   #5
hhibrownsbacker is offline hhibrownsbacker  United States
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Thanks guys, that helped allot. I can figure it out from here I think, now that I know what the heck Im looking at on those charts.
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Old 16th August 2016, 05:01 PM   #6
kevinkr is offline kevinkr  United States
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SSE sounds good BUT???
The series diodes on the plates of the 5AR4 do no harm and provide a lot of protection even for good NOS 5AR4 in the event of a multi-cycle power interruption or the cycling the power switch before the rectifier has fully cooled.

The odd readings have to do with how your meter interprets a half cycle rather than the full sine wave. Using a scope you will see a half cycle with the same peak amplitude (minus diode drop which is miniscule in this case) as the peak of the sine.

The output voltage on the cathode of the 5AR4 will not be measurably different with or without the series diodes.

I have lost Mullard and Telefunken 5AR4 working into close to the rated capacitance due in one case to a slighly intermittent power switch and in the other due to a very short duration power failure (a few seconds) - I'm relatively confident series diodes on the plates of these tubes would have prevented their failure.
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Old 16th August 2016, 05:05 PM   #7
wdecho is offline wdecho  United States
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Originally Posted by hhibrownsbacker View Post
Thanks guys, that helped allot. I can figure it out from here I think, now that I know what the heck Im looking at on those charts.
Give me the readings on your plates, the output tubes you are using and the K value of the OPT's and I will try and tell you what I would use from the chart.

On mine I measured 418V B+ with EL34 tubes and 5000K OPT's and settled on 400 ohm cathode resistors vs the 560 ohm I started with to be on the safe side upon first firing the amp up. I estimate the change increased my soundstage 50% more than I had before the change. It is worth the effort doing for anyone that has not adjusted their cathode resistor after building this amp. What it amounts to is you are biasing the output tubes higher and whether tubes or a Class A SS the sound is generally better the higher you go. George has provided the chart which is much appreciated.

It is not hard to tell if you get the bias too high. You will start seeing red plates or red patches on the plates. The chart should keep anyone safe before this happens.
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Old 16th August 2016, 11:16 PM   #8
hhibrownsbacker is offline hhibrownsbacker  United States
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Originally Posted by wdecho View Post
Give me the readings on your plates, the output tubes you are using and the K value of the OPT's and I will try and tell you what I would use from the chart.
I appreciate your effort. I originally had a set of KT88 plugged in but tried a set of EL34 and they seem more musical so Im going to go with them. The OT are Transendar 5000K, I got B+ of 452 (taken off of R4), cathode voltage of 34.6 and 35.2, plate voltage of 448.5 and 448(taken off pin 3), and cathode resistance of 548 and 549(560 resistor installed).

Last edited by hhibrownsbacker; 16th August 2016 at 11:23 PM.
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Old 16th August 2016, 11:57 PM   #9
wdecho is offline wdecho  United States
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You are set to go as is and nothing needs doing from what I see on the chart. Go to the chart EL34 and go the the first file that says B+V and find 450. The next file is Load Z and go to 5000. Now look at the RK file and from what I see 560 ohms is the correct value with the EL34 tubes. With the KT88's I would use 400 ohms for the cathodes.
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Old 17th August 2016, 12:21 AM   #10
hhibrownsbacker is offline hhibrownsbacker  United States
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Thank you sir, if you are ever in Fla, PM me, I owe you a beer or two or three, hehehe. Thanks again.
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