Difference bewteen ultralinear & triode mode?

[James Freeman]

I'm surprised the U/L triode switches aren't worn out in a couple of months..😀

So your amp should be versatile ..just like an egg 😀

Hmmmmm.....

You think I should mutilate my brand new amp the second it arrives or give it a chance stock for a couple of days? 😀
You know I got the itchy hands... don't push me...

 

[James Freeman]

Just curious to know is there any side effect or damage to the tube amplifier if we switch triode to pentode or vice versa when listening to music.

Never switch while the amp is on. Your ears, speakers or amp may be damaged.

DF96 can you please list the damage and reasons that can occur when switching a Triode/Pentode/UL switch while HV is on?

Will a standby switch that opens the HT (Plates and Screens only) is better than switching the amp completely which includes filaments and rectifier?
I guess the real question is what will cause more damage and strain, Power switch or Standby switch?

Switching the Power off (HV, Filament, Rectifier) for 5 seconds then On again, or switching a Standby off (HV only) for 5 seconds then on.
Switching the main Power strains the Power Transformer, Capacitors, Filaments, Rectifier, everything that needs current and causes CURRENT INRUSH.
While switching the Standby will strain the the standby switch itself because it's switching DC, but nothing before it (Filament, Rectifer, Caps).

Am I logical? Shed some light please.

 

[M Gregg]

please list the damage and reasons that can occur when switching a Triode/Pentode/UL switch

You will get a surge at switch over you are in effect turning the power tubes off then back on..as you flip the switch the contacts break then make.

If you power down and back up with a HT standby switch there are issues..

The Heaters are still hot at power up. But if the tubes are cathode biased then the cathode cap discharges and you get a surge at power up..
Its not such an issue with fixed bias as long as the fixed bias is kept up while the HT is off

The other issue is when HT is off there is no load on the PSU so the HT can float up to higher voltages then the supply caps can stand.

_______________________________________________________________________

with power down

The bias supply if its using fixed bias will now be down and have a power up time.

Any PTC thermistors may still be hot in the PSU so the surge limitation is not working.

There is always more but it gives you an idea..

If its cathode biased then the cathode cap will discharge through the cathode resistor and as the tube powers back up you get a charge surge.
(Because the heaters are still hot)

If you power down the supply (switch off and back on) the heaters are hot and there is no bias supply for a few seconds so the tubes sort of run flat out for a fraction of a second while the bias supply comes back up..(HT fuses normally blow)

The bottom line is heater power up time and surge suppression compared to cold start and hot start.

So HT standby switch with fixed bias is OK as long as the supply caps can withstand the voltage with PSU off load.
This is also one of the differences with a CCS in the cathode there is no cathode cap to charge (theoretically).

I have and do use HT standby switches with fixed bias with a PSU designed to work off load with no problem at all. Switching 8 power tubes at the same time
while using the standby switch and then switch between Triode pentode U/L etc. So not having to power down the whole amp and wait for it to cool down before change over. So in this instance the standby switch is switching the HT to the output transformer with no power supply caps or anything else.

Regards
M. Gregg

 

[M Gregg]

One other thought is,

watch out for DC coupling on any stages...(if there are any)
You don't want to effect DC bias conditions on circuits.

I'll shut up now..😀


Regards
M. Gregg

 

[James Freeman]

So what will put more strain on a Cathode biased Class A amp, Powering Off and On when hot, or putting it in Standby?
If I understand you correctly, the cathode caps will discharge in both situations, but what about the filter caps (if they can take the extra HT voltage) and PWT?
The less parts under strain the better.

I installed a soft start board (THIS) for my SS amp with couple of NTCs and a Relay, to protect my the amps (various parts) against inrush current, what about Tube amps?

 

[Chris Hornbeck]

I'd worry most about the dI/dT spikes made when switching current through the primary inductance. That's how auto ignitions make their big sparks from 12 Volts.

Chris

 

[DF96]

So what will put more strain on a Cathode biased Class A amp, Powering Off and On when hot, or putting it in Standby?

Define precisely what you mean by "Standby".

Most valve circuits can be happily powered off when hot or cold, and on when cold. Often, powering on when hot is OK but could create inrush problems and output transients. Curiously, this is precisely what some so-called 'standby' switches do!