New 6V6 Build - Suggestions Needed - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 1st October 2012, 02:16 AM   #11
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by SandyG View Post
Back again for some help on a 6V6 Project. I Mashed together a few different schematics and came up with the EZ10. Trying to make a pair of small mono-blocks for my office and figured I would try an all octal 6V6 based amp.
I looked at the photos and see a PCB. Did you actually built a printed circuit BEFORE you had a working prototype bread board. That requires more faith in your design than I ever have.

Do you have a scope? If so it should be easy to see where the amp is clipping. If I have to guess I'd guess you are not driveling the 6V6 with a large enough signal. Take out the NFB and add back the cathode cap that is now "open" and see if it still clips.
  Reply With Quote
Old 1st October 2012, 02:30 AM   #12
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Yep, made the boards up prior to trying the circuit. It was a pretty simple circuit so much could be done before saying the boards are worthless . I have 2 issues with the board, forgot to connect the 2 stages together on the SN7' (Pin 2 to 4) easy fix, and a lead spacing on a few caps are too narrow... oops one more forgot the resistor in the feedback loop if the capacitor is used on the bottom leg of the input (not sure I'll use the cap).

Half the fun was fitting all the parts to the board and then trying to get that to fit in a small 6"x10" hammond chassis with all the iron.

The EZ260 amp was a lot more complicated (Grommes 260A Clone), this one was not too bad due to low parts count and really simple design.

Just need to get a bit of time and fiddle with the parts to dial it in.

Yep, have a couple of scopes, I'm 99% sure it's in the first stage just due to the low plate voltage but will hit it with the probe and confirm.

Sandy
  Reply With Quote
Old 1st October 2012, 02:54 AM   #13
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Try 150k for the anode resistor of the first stage (6SL7), with the 1k cathode resistor. That should get you in the neighborhood of 90V. As a rule of thumb for a split load splitter/inverter you want the anode to be approximately 2/3 of the anode supply and the cathode at 1/3. I know everybody here is pushing their darling 6SN7 (mine too), but you may just need that little extra gain up front for some GNFB.

Last edited by cogsncogs; 1st October 2012 at 02:56 AM.
  Reply With Quote
Old 1st October 2012, 05:24 PM   #14
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Quote:
Originally Posted by cogsncogs View Post
Try 150k for the anode resistor of the first stage (6SL7), with the 1k cathode resistor. That should get you in the neighborhood of 90V. As a rule of thumb for a split load splitter/inverter you want the anode to be approximately 2/3 of the anode supply and the cathode at 1/3. I know everybody here is pushing their darling 6SN7 (mine too), but you may just need that little extra gain up front for some GNFB.
Ok, trying to learn to fish here Can you help with some of math so I can see how to calculate this?

One thing that I do have a question is that I see quite of few 6SL7's with the cathode resister in the 1.5k-3k range vs. the 1k that I 'picked' for this amp. Is the 1k value too low or is it not super critical??

In the 6SL7 GE Datasheet it shows the sample for the 'Resistive Coupled Amp' with a table of resistors which in most cases are > 1k.

One thing that did confuse me was that plate voltage target and Ebb are not the same, so in my case the measured Ebb was about 286v with the 270k plate resistor.

Learning as I'm going but hopefully questions are meaningful!

Sandy
Attached Images
File Type: png 6sl7gt-ge-sample.png (59.9 KB, 435 views)

Last edited by SandyG; 1st October 2012 at 05:28 PM.
  Reply With Quote
Old 6th October 2012, 05:58 AM   #15
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Ok found out a couple of things, 1st, amp making fair power, I calculated the power output wrong. OOPS Mistake.

Amp putting out 8.5VRMS into 7.8ohms resistive load, so about 9 watts of output before clipping.

Calculated the voltage drop across the input stages Cathode Resistor (R7 1K) initially at .7ma (.71v drop) with the 270k plate resistor.

After changing the plate resistor to 150k the voltage drop was right at 1ma for the input stage. Up from .7ma.

The phase inverter resistor are 103k (ran out of 100k's) and see a 105V drop across both R14 and R9. So about 1ma on each of the resistors. DOES this mean 2ma tube current????

Sandy
  Reply With Quote
Old 6th October 2012, 12:48 PM   #16
roline is offline roline  United States
diyAudio Member
 
roline's Avatar
 
Join Date: Sep 2010
Location: East Tennessee
The cathodyne is an in series device, so 1ma through it. It appears to be close to center biased, so how does it sound? and what can you get out it it before clipping?
__________________
SO many tubes, SO little time!!!
  Reply With Quote
Old 7th October 2012, 02:14 AM   #17
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Quote:
Originally Posted by roline View Post
The cathodyne is an in series device, so 1ma through it. It appears to be close to center biased, so how does it sound? and what can you get out it it before clipping?
It's putting out a bit over 9 watts as I calculated it. I have only tried it on a small speaker so can't say at all how it sounds as yet. Will need to put it in the chassis before I can move the mess of wires near some reasonable speakers.

Is the 1 ma too low for the phase inverter stage? Seems like the amp should do a bit more then 9 watts before it gets into clipping. Or is this common for 6v6 amps?

Power supply is much larger then needed as well as the choke (7H) and 15w output transformer (All Edcor).

I'm running an 8K impedance ultra linear edcor output trans, might I have been better off running something lower like a 5k?

I have also not messed with the negative feedback either, but signals look very clean just can't comment on sound quality as yet.

Sandy
  Reply With Quote
Old 7th October 2012, 03:24 AM   #18
rongon is offline rongon  United States
diyAudio Member
 
rongon's Avatar
 
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
I have the plate curves for 6SL7GT. I attached them below.

You gave us voltages with "no load." Does that mean there were no tubes in the sockets? Or does that mean there was no signal going into the amp? Could you put the tubes in, power up the amp with no signal applied, and give us the voltages at all the tubes' plates and cathodes, and the voltages of the HV feeds?

With HV2 at +326V, and +200V on the plate of the cathodyne 6SL7, that means there's 126V dropped across the 100k plate resistor, which means 1.26mA through the cathodyne. The 100k resistor in the cathode would also drop that same 126V. So...

126 + 126 = 252V dropped across the two 100k resistors. That leaves a plate-to-cathode voltage of only 70V across the 6SL7 (252 + 70 = 326). With only 70V plate voltage and 1.25mA across the tube, that would put the tube down near zero bias, cathode to grid. Crunch!

I think we need measured voltages with the circuit operating before anybody will be able to give you useful advice.

That circuit should work fine, even with 6SL7 as the voltage amp and cathodyne phase splitter. It looks to me like the cathodyne should have no more than about 0.7mA through it. I think you want to get the bias on the 6SL7 up to about 1.5V (cathode positive to grid).

--
Also wanted to add -- After looking at the 6SL7 curves, it looks to me that this is a tube that needs a high B+ to work with. The loadline for B+ = 300V and a 100k plate resistor looks very steep, which would give you higher distortion, with a higher proportion of 3rd harmonic likely. Redraw the loadline with 400V and a 270k plate resistor and things look much better.
--
Attached Images
File Type: jpg 6SL7GT_curves.jpg (682.4 KB, 327 views)

Last edited by rongon; 7th October 2012 at 03:40 AM. Reason: second thoughts...
  Reply With Quote
Old 7th October 2012, 11:59 AM   #19
pointy is offline pointy  United Kingdom
diyAudio Member
 
pointy's Avatar
 
Join Date: Mar 2009
Your problem may be due to the heater supply for the 6sl7-gt, as it is a twin triode. With some values if this type when they are use one half for one channel and other for the otherchannel.One of the channels is found to have less gain. This happens because the heater goes in to one cathode and then in to the next. Some thing you can try is if you have a spare 6sl7-gt using one triode section from one of the tubes for v gain and the other for the inversion..
  Reply With Quote
Old 7th October 2012, 12:50 PM   #20
pointy is offline pointy  United Kingdom
diyAudio Member
 
pointy's Avatar
 
Join Date: Mar 2009
after looking at the setup that you have you should be able to check for this by switching over the heat supply y-x to x-y and then measure the gain to see if it is the same.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Build guitar amp with 2 6L6 or 4 6V6? TubeTweaker Instruments and Amps 11 15th August 2012 12:01 PM
Advice needed on new 6L6 ro 6V6 SE or SET build GloBug Tubes / Valves 39 23rd November 2011 04:22 PM
A little help with 6v6 screen needed. lazzer408 Tubes / Valves 15 28th February 2011 07:32 PM
At Last....First Build Complete...6V6/6SL7 cbj591 Tubes / Valves 9 31st July 2010 01:51 AM
6v6 music machine build help! tubo Tubes / Valves 26 5th November 2009 04:34 PM


New To Site? Need Help?

All times are GMT. The time now is 10:17 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2