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OPUS 5.0 A Modern Mullard
OPUS 5.0 A Modern Mullard
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Old 6th October 2010, 09:20 PM   #261
The Space Egg Corp is offline The Space Egg Corp  England
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Quote:
Originally Posted by SGregory View Post
capacitance.
Hi Scott

Answer a tubie newbie question for me.

This might seem like a daft question looking at your power supply.

Obviously in SS there's no such thing as too much capacitance.

But in tubes is it possible to use too much and have problems at switch on with damaged plates or filaments.
Have tried to look into this today but can't find the answer.

I see you have two switches to let heaters warm before HT goes on.

Are the motor runs on the lower voltage pre tubes, and the biguns on the main HT ?

And what caps have you got on your heaters.

I should go to bed and stop thinking about amplifiers !!!

Simon...
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Old 6th October 2010, 09:48 PM   #262
SGregory is offline SGregory  United States
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Its a mix.
Actually there is a surge surpressor prior to the HV schotkey diodes. In this case the diodes are plenty big enough, but the PT will complaign. For tube rectifiction there is a limit on the size of the initial capacitor depending on its construction. That information is spelled out in the tube datasheet for each one. The problem is not only during start-up but mainly during normal operation. A tube rectifier does a nice job of self current limiting itself up to a point while it warms up.

The filament switch is to warm the filaments of the amplification tubes prior to B+. It is suppose to stop cathode stripping. I really don't use it much. Personally, I just flip them on simutaneously most of the time. I am sure both sides of the cathode stripping camp will have something to say here so flame on. The red and black switch does look good though ;-)

As for the motor runs, they are used throughout the PS. They are the initial capacitor prior to the choke, a bypass cap for the big honkers, a resivour for the LTP and finally a resivour for the input tube.

For the heater caps, those are axial mkp but in truth, ceramic will do much better and be more compact in this application. It would be best to have those tie direct to the metal socket mounting ring for ground instead of away as they are built. I got them by accident and at a bargain so I kept them.

Sleep Tight.
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Old 26th March 2011, 01:31 AM   #263
boywonder is offline boywonder  United States
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I'm slowly building up sub-assemblies for a mutation of this build and I have a question about the B+ and C- rails. I'm building a stereo chassis and I have the option of using separate B+ and C- rails for each channel or having the channels share rails. Any disadvantage to sharing the rails? It would save space, diodes & caps, but I'm OK with leaving them separated.
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Old 26th March 2011, 11:34 AM   #264
SGregory is offline SGregory  United States
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I can't see a problem with sharing the C- rails. What voltage are you setting C- to.
I would be careful with Sharing B+.
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Old 26th March 2011, 02:36 PM   #265
boywonder is offline boywonder  United States
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Default I meant the Mosfet drain rail........

Sorry, I meant the Mosfet drain rail B1+........

For C-, I have a small hammond isolation transformer 1:1, so it'll be rectified and smoothed mains voltage, around -150V
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Old 27th March 2011, 02:18 AM   #266
SGregory is offline SGregory  United States
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Good C- number just make sure you have good decoupling on the bias pots. I don't think you will have a problem for the mosfet B1+ sharing channels since they are on a CCS.
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Old 30th June 2014, 06:39 PM   #267
stonehome is offline stonehome  United States
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Default Another Opus 5.0

I think I am close to completing SGregory's "Opus 5.0". I say I think I'm close because another problem has shown itself, as soon as I input a signal there is a high frequency buzz, almost a whistle, coming from the output transformer. I have the oscilloscope connected across the speaker terminals with an 8 ohm load attached. The signal generator is connected to the amps input rca and a 2.5kHz 1.414Vpp signal applied. I have only left it for a second because of the buzz. Output tube bias is set at 0.45V and all other voltages are where they should be.

As I was writing I remembered about a month ago I had the amp connected briefly to speakers and played music with it connected to my phone. I noticed no transformer noise then. That's the problem with DIY, when IQ have to take a break to work it takes a while to remember where I was. I am going to go over it again and check any changes I've made since then.

If anyone has experienced anything similar please let me know.
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Old 30th June 2014, 06:43 PM   #268
stonehome is offline stonehome  United States
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It will only let me upload one photo at a time.
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Old 30th June 2014, 06:54 PM   #269
stonehome is offline stonehome  United States
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One more
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Old 1st July 2014, 01:04 AM   #270
kevinkr is offline kevinkr  United States
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OPUS 5.0 A Modern Mullard
500mVrms (1.4Vpp) is a pretty large input signal - I would not be surprised if this represents something close to full power, winding buzz and magneto-striction in the core are common at higher power levels. Did you measure the output voltage?
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