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Old 16th May 2011, 05:26 PM   #131
Desmo is offline Desmo  Denmark
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I've done one more upgrade... I bought some more of the Obbligato 2,2uF caps used in the output so the cap is now 6 x 2,2uF tinfoil...

First impressions are very good, even without burn in of the new caps. Together with the Duelund CAST I use as input caps these upgrades truly make a difference...


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Old 22nd May 2011, 09:00 AM   #132
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Just a question regarding the bias adjustment. Is the bias adjustment for left and right channels supposed to be independent? In other words, is adjusting bias on one channel suppose to affect the bias on the other?
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Old 23rd May 2011, 04:16 AM   #133
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by DECKY999 View Post
Just a question regarding the bias adjustment. Is the bias adjustment for left and right channels supposed to be independent? In other words, is adjusting bias on one channel suppose to affect the bias on the other?
There will be a slight interactivity, as both channels load the PSU jointly and if one channel is widely out, brining it in line will slightly shift the channel that is already set correctly.

Also, there is a time constant (a fairly long one) in the setting.

Ciao T
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Old 23rd May 2011, 06:13 AM   #134
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I was rechecking the bias recently and realized that it was quite a bit out of the optimum 120V. This is after a week or so from the last adjustment. One channel was ~160V and the other 110V. Before adjustment was quite easy (with the obvious time constant or "inertia" in voltage stabilisation, how I call it) but now the channel interdependence was so strong that I could not bring them on stable 120V at all, even after several hours of work. Is maybe something wrong with the auto bias circuit?
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Old 23rd May 2011, 10:57 AM   #135
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I tried again. There is something wrong with one channel bias regulation. If I adjust left channel to 120V then the right one increases to 230V and it that voltage does not react on any of the right channel pot adjustment (from one extreme to another). If I make right channel to be around 120V then the left one drops to 40V. Both channels are sensitive to the left pot but so much to the right one. ANy ideas?
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Old 23rd May 2011, 11:52 PM   #136
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I just want to add that I managed to replace the heater voltage regulators. The old LM1084 from ebay were fakes. The new ones from element 14 work quite well with 2A3 valves and 0.33R resistors on the AC lines. Regulation is 100% stable at 2.5V. I installed these heatsinks by bonding them to the sides of the original ones by Arctic silver thermal epoxy
Click the image to open in full size.

With them temperature was around 60C after more than 1 hour of operation and room temp was ~23C. So, looks very promising and I have to swallow my own words for being doubtful about the feasibility of using 2A3 valves.
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Old 24th May 2011, 01:41 AM   #137
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by DECKY999 View Post
I tried again. There is something wrong with one channel bias regulation. If I adjust left channel to 120V then the right one increases to 230V and it that voltage does not react on any of the right channel pot adjustment (from one extreme to another). If I make right channel to be around 120V then the left one drops to 40V. Both channels are sensitive to the left pot but so much to the right one. ANy ideas?
It sounds maybe one of the CCS (Ixys 10M45) has thrown the towel, they do not like to see the output shorted to chassis.

Ciao T
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Old 24th May 2011, 06:29 AM   #138
Desmo is offline Desmo  Denmark
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Quote:
Originally Posted by DECKY999 View Post
I just want to add that I managed to replace the heater voltage regulators. The old LM1084 from ebay were fakes. The new ones from element 14 work quite well with 2A3 valves and 0.33R resistors on the AC lines. Regulation is 100% stable at 2.5V. I installed these heatsinks by bonding them to the sides of the original ones by Arctic silver thermal epoxy
Click the image to open in full size.

With them temperature was around 60C after more than 1 hour of operation and room temp was ~23C. So, looks very promising and I have to swallow my own words for being doubtful about the feasibility of using 2A3 valves.
This is very much in line with my experience based on my ''proof of concept'' with some aluminium bonded to the existing heat sinks. I have been running this set-up for several weeks now with 2a3 and there has been no unstability since then... It works
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Old 24th May 2011, 08:32 AM   #139
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Quote:
Originally Posted by ThorstenL View Post
Hi,



It sounds maybe one of the CCS (Ixys 10M45) has thrown the towel, they do not like to see the output shorted to chassis.

Ciao T
That is what I was afraid of. Is there any chance that you or Brian can send me a pair of these. I cannot find them in element14 or RS catalogue and Digikey is not shipping them to Australia (manufacturers restrictions they say).

I appreciate your help.
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Old 2nd June 2011, 04:49 AM   #140
jacklee is offline jacklee  Hong Kong
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Default Tram2 Operating Points

Hi,

I just joined the Tram2 family and would like to share some initial observations.

Initially I used TJ Globe 45s and WE 274B rectifier tubes as I happen to have them on hand. This setup works fine except for a low-level hum that I cannot get rid of. After some trouble-shooting I concluded the hum is generated by the amp itself and not due to other components or ground loops.

I also tried shielding the rectifier and the output triodes with a graphite tube shield connected to the signal input ground but no luck. Then I found a RCA 5U4 in my tube stash and tried it on replacing the WE 274B and voila the hum is gone completely.

So in this case the hum is either due to EM leak or different operating points resulting from the WE274B. To investigate this further I installed a UX4 test socket adapter to the TJ45 and measured:

- Filament voltage is 2.56V
- Bias current is 31mA (w/ 274B)
- Grid to filament ground is ~-8V (w/ 274B) and ~-10V (w/ 5u4)
- Plate to filament ground is ~80V (w/ 274B) and ~100V (w/ 5u4)

So it seems changing the rectifier could change the operating point of the output tubes. Is this normal? The RCA 5u4 does measured much stronger than the WE274B in my tube tester. Also, are the measured voltages/currents within spec? In particular is the plate-to-ground too low (~100V vs 120V)?

I also noticed that upon turn-on the plate-to-ground and grid-to-ground voltages are much higher, ~200V and ~-60V respectively, and then slowly converge to the values listed above.

One final question: do I need to adjust anything if I replace the 45 output tubes with 2A3? The manual seems to suggest it is plug and play but I want to make sure first.

Thanks.
Jack
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