Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

His Master's Noise: A Thoroughly Modern Tube Phono Preamp
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th July 2017, 05:56 AM   #411
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
Okay, now im understanding, how the 5k6 resistors are arranged. For durable using i would use a little more as 5W. I heared, a rule is, to use not more than a quarter of the load.
The 158V for the 160V regulator is okay. I think a little more input as 198V were better for filtering. But for testing its okay.
  Reply With Quote
Old 14th July 2017, 05:58 AM   #412
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
The heater cannot drag the voltage down. You can wire the heater later, to pull them up to the 65V. That is no load. The heater sees only the voltage.
  Reply With Quote
Old 14th July 2017, 06:03 AM   #413
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
Interesting is your transformer. You wired the 2 x 250V parallel? So you got (2 x 80) 160mA x 0,7 = 112mA?
Your hum under load comes from where?
  Reply With Quote
Old 14th July 2017, 06:04 AM   #414
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
One more word to the regulated PS. You can test without load, cause the voltage is the same. It will drop under load not more than 2V.
  Reply With Quote
Old 14th July 2017, 06:27 AM   #415
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
If the Voltage(s) are okay, wire only the 260V (and heater) to the HMN-Board. Then measure the voltage about R3 (1k). After a few seconds the voltage have to go to nearly 20V. Gratlations, the first stage is working.
Do the same with the second stage (only the second stage). The neon bulb will light on and after a few seconds go out. Instead the LED will slowly light on (not so bright).
Measure about R12 (1k) nearly 10V will be right. The first half of the second stage works.
Now measure the drop about your preresistor 5,6K. This drop minus 56V (for the 1st half/2nd stage for 10mA) gives the working current for the cathode follower.
You wrote the drop is 115V. This gives 59V/5,6k = voila nearly 10mA = perfect.
Now enable both stages and pull up the heater.
Its weekend, so enjoy the sound.
  Reply With Quote
Old 17th July 2017, 04:42 PM   #416
mrdave45 is offline mrdave45  United Kingdom
diyAudio Member
 
Join Date: Oct 2010
Location: Kent
Default heater cathode voltage

Thanks frank, ordered some more bits, will install them tomorrow when they arrive.

I dont think i understand this heater to cathode voltage correctly. Ive been looking into this due to wanting to test without heater elevation.

A few assumptions i want to make sure are correct.
Section 2 of the 6922 is the buffer (cathode follower) with the cathode at 95v.
Section 1 of the 6922 is the second gain stage with the cathode at 1.7v
Vkf is the notation for cathode heater (presumably f for filament)


In the article

"The more well-known twist is the use of R30 and R31 to elevate the heaters 65V above ground. This has two salutary effects - first, it reduces the heater-to-cathode strain of the cathode follower. For that tube, the cathode is roughly 95 volts above ground. Without this heater elevation, the heater-to-cathode voltage well exceeds the 50V limit for triode section one and strains the limits of triode section two. With 65 volts of elevation, the heater-cathode potential for the follower is a balmy 30V. "

I looked up the datasheet for the 6922eh. It seems that this can have the heater to cathode positive or negative 200v. So for this tube i dont think this applies.

I looked up the ecc88 and found a philips ecc88. Im assuming this is a similar tube to the one sy uses. This has the following

Vkf = 50v max
Vk'f (k' pos; f neg) = 150v max

I have also seen from telefunken CCa
Uf/k+ = 150v
Uf/k- =100v

The way the article is worded it looks at if Vkf is when the cathode is positive relative to the heater and Vk'f is when the cathode is negative relative to the heater.

I would have thought that Vk'f (k' pos; f neg) = 150v means that the cathode can be a maximum of 150v higher than the heater.

Even so, if the heater cathode limit for the follower is 50v and thats how to read the spec sheet, i can see that the 95v exceeds this and so the heater elevation fixes it but why does this strain the other section without the heater elevation? Surely the cathode for the second gain stage would be at ~1.7 volts and the heater at somewhere between -6.3v to zero or zero to +6.3v. so only a few volts difference, well within any of the specs.

Ok, going on the siemens D3a. The spec sheet i found for that has this.

Voltage between cathode and heater
Cathode positve Vkf = max 120v
cathode negative Vkf = max 60v

To me this is implying that if I elevate the heater to +65 volts then the cathode is going to be about 64v below the heater and is likely to be damaged.

I've catastrophically misunderstood something here but Im not sure where ive gone wrong.
  Reply With Quote
Old 18th July 2017, 12:26 PM   #417
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
Hi Dave,

the 6922 is similar to ECC88 or E88CC. where do you found the information about 200V for the Ufk?
RCA, Siemens and Telefunken said -60V and +120V
Phillips -90V and +120V.
The datasheets for the 6922 and E88CC are the same.
  Reply With Quote
Old 18th July 2017, 12:29 PM   #418
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
The datasheet for the CCa from Telefunken is also the same. There is only one piece for three Tubes.
  Reply With Quote
Old 18th July 2017, 12:32 PM   #419
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
Okay, I found the datasheet for 6922 from EH. It think the insulating layer between cathode and heater is better. So the Ufk is higher.
  Reply With Quote
Old 18th July 2017, 12:53 PM   #420
frankwilker is offline frankwilker  Germany
diyAudio Member
 
Join Date: Nov 2011
Location: Duisburg
You are right, the cathode can be the Ufk higher than the heater. Otherwise the isolation between heater and cathode can be damaged or affects a hum or other noises.
All you wrote is right, but you measuring is false. The voltage about Rk is 1,7V. Now measure from Ua to k and you found nearly 140V? So Uk is Ua - Urk (I hope all notations are right). Its only a thinking fault.
So the voltage is above the Ufk. To heighten the Heater gives a smaller difference. But attention, the heater is not connected to Common. Only about the voltage dividier. (C is much to great. Enough is up to 10 f.)
A cathode follover is in the most cases no problem. The voltage is a little higher than the half of Va, here like 90V, the heater is 65V, so the difference is 25V.
I hope someone understand my bad english, sorry.
  Reply With Quote

Reply


His Master's Noise: A Thoroughly Modern Tube Phono PreampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Low noise transistor and noise figure Real_Macgyver Solid State 28 27th July 2012 10:42 AM
noise planarboy Analogue Source 2 11th February 2008 09:06 AM
Still have noise. pjanda1 Chip Amps 40 17th March 2006 04:16 PM
Help with noise davidlzimmer Chip Amps 25 5th March 2006 10:39 PM
Noise Bukitoo Analogue Source 2 17th March 2004 03:37 PM


New To Site? Need Help?

All times are GMT. The time now is 05:13 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki