Problem with my Darling! - 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 23rd February 2005, 09:12 AM   #11
diyAudio Member
 
Join Date: Feb 2005
Location: Knoxville TN
Yes, Philip, something is very badly out of whack here. If you put 1vAC into the 6j4, you ought to have less than 55 vAC out. With .088vAC in, you'd get less than 6.8vAC out. It is *impossible* to actuall get readings such as you have, no matter how many times you check them.

Let's solve that problem first; you have something wrong with your test setup.

How do you know that the source is putting out a sine wave? What are you using to check the voltages and what scale are you using for each reading (only* on the 6J4? Also, tell us again what the reading is at the cathode of the 6J4 (I'm in the reply screen and can't see the main thread).

You would have a far better chance of working this out if you could find some way to get a good sine wave at 1vAC into the grid of the 6J4. Do you have a friend with a real signal generator?

Don't even think about the output stage at this time.

Cheers/Fader
  Reply With Quote
Old 23rd February 2005, 02:31 PM   #12
diyAudio Member
 
philipbarrett's Avatar
 
Join Date: Feb 2005
Location: Dallas, Texas
Send a message via AIM to philipbarrett
John - thanks for your help.

I think the input math is correct, my iPod is delivering 880mV (not 88mV) which by your math of 1V in = 55V out makes my reading of 34V out about right?

I am measuring with the Radio Shack RMS multimeter in "auto" and have the Spectra-Foo FFT analyzer running on my Mac to confirm the sine wave.

The cathodes on the 6J4s read 2.7VDC each.

I am trying to get time on a scope & generator today and will hit the input with 1VAC.

Thanks again.

Philip
  Reply With Quote
Old 23rd February 2005, 02:54 PM   #13
diyAudio Member
 
Join Date: Feb 2005
Location: Knoxville TN
OK, Philip,

That last sounds all good. You don't need to sue a signal generator now that we've determned that you've got nearly a volt and that the sine wave is good. Better (moe convenient) test gear is nice, but now necessary if you've got *something* that yoiu can trust.

So, you've got 34vAC out of the 6J4, so that's all good. Bias sounds good, and so did plate when we were looking at that.

Now for the output: Bias sounds good as toes grid drive. E can't remember plate, but I think that was good. So, was the 10V or so output you mentioned initially the AC riding on the plate voltage? Or was it the voltage at the 8 Ohm speaker terminals? I suspect that it was the former. If so, and your tubes are good, we have a serious problem.

Try this: With the signal applied to the input, put your RS DVM on the AC scale that suits the grid and tell it to do relative (dang, too bad that DVM dosn't have a dB scale!!!). Now move to the plate and report the relative reading, + or -.

Though I don't believe that two 1626s would have gone bad in exactly the same way and value, we can't dismiss the possibility. Get another one, AAMOF get a pair, as you'll need them when you build your Parallel Darling :-)

Let's see if the new ones are "similarly failed" ;-)

Cheers/Fader
clutching at straws :-)
  Reply With Quote
Old 23rd February 2005, 08:24 PM   #14
diyAudio Member
 
philipbarrett's Avatar
 
Join Date: Feb 2005
Location: Dallas, Texas
Send a message via AIM to philipbarrett
OK - did a full bench test today using 1KHz at 1 V as a test source. All is fine until we reach the plates of the 1626s. At that point the gain disapears and the signal is heavily clipped. We took some current readings, measuring the Plate at 23mA at idle, 37mA with signal applied and the Cathode at 18mA under idle. This seems high, plus the 500R/5W resistor is getting pretty hot.

My friend with the test gear is also suspecting the tubes so I will take your advice & order another pair & see what happens.

In the meantime I might start my phono pre-amp, any suggestions?

Thanks, your time is really appreciated.

Philip
  Reply With Quote
Old 23rd February 2005, 09:52 PM   #15
diyAudio Member
 
jeff mai's Avatar
 
Join Date: Aug 2002
Location: Melbourne
Something to check - is the 1626 grid at 0VDC with no input signal? I'm thinking maybe leaky coupling caps could cause the problem. Maybe not but worth a look. I'd also measure the cold value of your cathode R just to make certain it hasn't gone weird.

Although this probably isn't the problem, 880 mVrms input will try to drive the grids of the 1626 well positive relative to the cathode at your bias point. This will do weird things to the operation - bias voltage and current will shift, grid current will start - not good. If you want to ensure "normal" operation while testing, 250 mVrms input is more appropriate.
  Reply With Quote
Old 23rd February 2005, 09:56 PM   #16
diyAudio Member
 
Join Date: Feb 2005
Location: Knoxville TN
Dang, Philip,

I just spent 10 0minutes talking about phono and line stages and i hit some wrong key and it all went into the bit bin somewhere.

I'll simplify a good bit here:
Do you plan to scratch-build or buy kits?
Do you plan to build a line stage?

I have strong opinions on both these items, and will go on if you wish :-)

Cheers/Fader
  Reply With Quote
Old 23rd February 2005, 10:46 PM   #17
diyAudio Member
 
philipbarrett's Avatar
 
Join Date: Feb 2005
Location: Dallas, Texas
Send a message via AIM to philipbarrett
Actually, I started a new thread since this is moving OT, but anyway;

1) scratch build
2) yes, I will build a line stage but the plan is to initially drive my Darling (assuming she'll ever work) with the RIAA pre and then at least I'll be listening to vinyl through my (yet to be built) Fostex based speakers.

The whole plan is to have built as much of a complete system as possible with my own fair hands! I'll leave the CD transport & DAC for later, likewise the turntable but hey it's a start.

P
  Reply With Quote
Old 23rd February 2005, 11:19 PM   #18
diyAudio Member
 
Join Date: Feb 2005
Location: Knoxville TN
Tood Show, Philip,

I'll nove this over to the other thread, but will stand by on the Darling thread to await news and to offer help.

Cheers/Fader
  Reply With Quote
Old 25th February 2005, 06:28 AM   #19
diyAudio Member
 
Join Date: Feb 2005
Location: Knoxville TN
Philip,

I just thought abut grid current and signed on to suggest coupling caps. Readingabove, I'll just second jeff's suggestions.
  Reply With Quote
Old 25th February 2005, 01:12 PM   #20
diyAudio Member
 
philipbarrett's Avatar
 
Join Date: Feb 2005
Location: Dallas, Texas
Send a message via AIM to philipbarrett
Thanks guys! I'm waiting on some new tubes too. The coupling caps would be the 27uF films connecting the 6J4 plate to the 1626 grid I assume?

Philip
  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
A Darling.......ton Story .... east electronics Solid State 19 12th November 2011 12:12 PM
Darling 1626 amp rca9449 Tubes / Valves 9 7th October 2008 06:33 PM
which project for a darling amp kalinowski Full Range 4 28th May 2008 09:30 PM
Darling in Europe... (110 vs. 220) opopanax666 Tubes / Valves 12 31st March 2008 08:26 AM
Darling monoblocks Greyskale Tubes / Valves 3 14th March 2008 12:25 AM


New To Site? Need Help?

All times are GMT. The time now is 11:38 AM.


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