When is it advisable replace PI valve?

[Kuga]

I heard from some techs when you need replace power valves It's advisable replace PI valve too. What do you think about It?

 

[PelliX]

I heard from some techs when you need replace power valves It's advisable replace PI valve too. What do you think about It?

When it's knackered. Get a valve tester or go by ear.

 

[Kuga]

When it's knackered. Get a valve tester or go by ear.

I built a ECC83 valve tester. I checked all my ECC83 valves. Some ones on PI position looks like suffer more stress.

 

[PelliX]

Some ones on PI position looks like suffer more stress.

That can well be the case, depending the amp. The PI is often hit relatively hard, depending on the topology.

 

[Pete Farrington]

I built a ECC83 valve tester. I checked all my ECC83 valves. Some ones on PI position looks like suffer more stress.

You know what you test rig is showing, whereas I'm not sure.
Can you explain what's being shown, and how analysis of the readings has led you to come to that conclusion?

I don't think most common LTP circuits put their triodes under particularly stressful operating conditions.

See https://www.aikenamps.com/index.php/technical-q-a

"Q: Do I need to replace my driver tube every time I replace my power tubes?
A: No. This is an "old wive's tale" propagated by the tube vendors who want to sell you more tubes. The "driver" tube, or phase inverter as it is more appropriately known, is under no more stress than any of the other preamp tubes. The output stage of a normal guitar amplifier is AC-coupled, class AB1 or class A1. The "1" suffix indicates that the tubes do not draw grid current during any portion of the input cycle. A "2" suffix indicates grid current during some portion of the cycle, as in class AB2. Since almost all guitar amps are class AB1 or A1 (it takes a DC-coupled cathode-follower or interstage transformer to be able to drive the power tubes into the positive grid region), the phase inverter does not have to supply any current to the grids (it can't really source current anyway - it only sinks current through the plate load resistor, which is quite large, and inherently limits the plate current to a few mA). The AC coupling (capacitor coupling) between the phase inverter and the output tubes precludes any flow of grid current anyway. The output tube grids will merely act as a grid clamp, shifting the bias downward as the output is driven harder. This in no way stresses the phase inverter tube. In addition, the plate load resistors and the bias current in a typical phase inverter are identical to the preamp stage values, indicating that they are operating in the same area, dissipation-wise, so they cannot be "wearing out" any faster. In fact, the reverb driver tube on a typical amplifier is dissipating more power than the phase inverter, and should be replaced more often, if anything. Don't be misled by the higher plate voltage on the phase inverter either, because the cathode is usually sitting somewhere around 30V - 100V above ground, which lowers the plate-to-cathode voltage by that amount. The plate-to-cathode voltage is what determines the power dissipation of the tube, not the absolute plate voltage."

 

[21fret]

A: No. This is an "old wive's tale" propagated

yeah 6.3 megatons of the old bags’ hatred towards your favorite pastime. might need more tubes, (or break out that 100w).

 

[Kuga]

You know what you test rig is showing, whereas I'm not sure.
Can you explain what's being shown, and how analysis of the readings has led you to come to that conclusion?

I don't think most common LTP circuits put their triodes under particularly stressful operating conditions.

This valve tester works prety same condicions as a valve amp. It has same power suply like a Madamp J5MK1. I did many test with ECC83/12AX7 valves. New ones, bad ones, balanced, etc... It test anode voltage and anode current on each triode. I test each triode with about 350Vdc. You can see on B+ display. You can see anode voltage on each triode on anode display using a toogle switch. I test anode current on each triode. I use this schematic from this youtube video where he explain It. He talks just about anode drop voltage on each triode but you know a drop voltage has relation with current. If not a drop voltage on anode no anode current. No voltage and current on cathode too. I realise If you have less than 1mA on one anode a valve sounds weak. A new ECC83 valve has about 1,25mA on each triode If you use this schematic. A balanced ECC83 has same anode current and same anode voltage on each triode. I tested many ECC83/12AX7. Current production ones and NOS ones. This tester don't show If a valve sounds good. It don't show If a valve it's noisy. It show how a valve is working. It show how fast anode get max current on each triode. A good condition valve quickly is working. A tired valve needs some seconds to show max current on each triode. You can see how quickly is a valve working with analog current meters. I can use a DMM to test current on each triode as well. I get a super acurated readings with a DMM. It has two toogle switch to open the circuit then you close the circuit using a current meter to get current readings.

It has three transformers. One for HT. One 12Vdc 500mA for valve heater. One 5Vdc cellphone battery charger for screen displays.

 

[Matthews Guitars]

Replace it when a new one makes the amp work and sound better. Every so often, try out a new one. If you don't hear a difference, put the old one back in and keep running it.

 

[Kuga]

Replace it when a new one makes the amp work and sound better. Every so often, try out a new one. If you don't hear a difference, put the old one back in and keep running it.

You are right. But with this tester I know and I can see why a valve sounds weak and I need replace a ECC83/12AX7 valve. I can know If a preamp valve it's ok faster than by turning on and playing an amp.

 

[Pete Farrington]

It test anode voltage and anode current on each triode

There's meters under the following labels
HTVol
B plus
ANODE
Could you explain what they're measuring?

 

[playloud]

If the amp sounds like "Mod 7", then one half has failed...

 

[nortiks]

I have a number of NOS and new current stock 12AX7, 12AT7, 12AU7 and a mismatch between the two triodes is the rule. The exception is when they are pretty close...which of course you can pay extra to get. So that needs to be considered when measuring a mismatch in a used tube. If you don't know 100% they were matched when new, which is improbable, then you can't jump to the conclusion that one side is taking more wear and tear when you measure the mismatch in a used tube.

 

[Kuga]

There's meters under the following labels
HTVol
B plus
ANODE
Could you explain what they're measuring?

HT voltage display show when HT voltage it's on. When it's on 257-259 Vca I know I'm testing at 230Vca. I use a variac and I use an isolated transformer with It. B plus display show valve suply. Anode display show anode voltage. If anode display voltage it's same like B plus display voltage on one triode I know this triode don't works.

First I put a valve on the socket then turn on switch on one side. The switch on the side turn on 12Vdc heater suply and turn on 5Vdc screen displays. After obout 10 seconds I can see on current filament display a consume about 0,150 A. A heater use more than 300mA when filament is cold. Then I can turn on HT voltage switch to get mesuraments. If a triode it's ok I can see max anode current in two seconds after I turned on HT voltage switch. If needs 5 seconds to show his Max anode current this triode it's worn out. When a triode it's worn out show less than 1mA

 

[Kuga]

I have a number of NOS and new current stock 12AX7, 12AT7, 12AU7 and a mismatch between the two triodes is the rule. The exception is when they are pretty close...which of course you can pay extra to get. So that needs to be considered when measuring a mismatch in a used tube. If you don't know 100% they were matched when new, which is improbable, then you can't jump to the conclusion that one side is taking more wear and tear when you measure the mismatch in a used tube.

I tested current production balanced valve from TAD(two). They show same anode voltage and same anode current on each triode. They are used phase inverter valves. Also I tested an older than me green logo Philipps ECC83 that tested great. This valve sounds awesome. Some current production valves I tested worn out really fast (7025 12AX7 from TAD) Less than three years of use on V1 position. I tested very used Marshalls ECC83 from '90s. Some ones still ok.

 

[Pete Farrington]

HT voltage display show when HT voltage it's on. When it's on 257-259 Vca

I guess that's the mains transformer HT winding V AC? ca. is often used as an abbreviation for 'circa' = 'about'.

Then I can turn on HT voltage switch

What's the point of switching the HT separately?

If a triode it's ok I can see max anode current in two seconds after I turned on HT voltage switch. If needs 5 seconds to show his Max anode current this triode it's worn out

How have you come to this understanding, what technical reference / evidence have you used to make this conclusion?

I tested current production balanced valve from TAD(two). They show same anode voltage and same anode current on each triode. They are used phase inverter valves

By 'phase inverter' do you mean 'long tailed pair' LTP?
If so, you seem to be overlooking the self balancing nature of the circuit.
What's your reference / evidence that, compared to functional but not particularly well matched triodes, well matched triodes result in a better audio signal match at the LTP anodes?
There's a lot of negative feedback within a LTP, that is devoted to delivering balanced outputs.
Consider that a pair of 12AX7 triodes have a potential cascaded gain here of about 70dB, whereas the actual signal path grid to anode gain is about 35dB.

 

[Kuga]

What's the point of switching the HT separately?

I can see If valve heater it's ok. When filament is consuming about 150mA I know valve it's hot to work. I have one it's using 350mA all time. This valve don't works.

How have you come to this understanding, what technical reference / evidence have you used to make this conclusion?

Testing many valves. New ones or good condition ones show max current anode faster than worn out ones. Looks like a good one quickly is able to works. Do you think this not can be correct?

By 'phase inverter' do you mean 'long tailed pair' LTP?
If so, you seem to be overlooking the self balancing nature of the circuit.
What's your reference / evidence that, compared to functional but not particularly well matched triodes, well matched triodes result in a better audio signal match at the LTP anodes?
There's a lot of negative feedback within a LTP, that is devoted to delivering balanced outputs.
Consider that a pair of 12AX7 triodes have a potential cascaded gain here of about 70dB, whereas the actual signal path grid to anode gain is about 35dB.

I mean ones that sellers sell as a balanced phase driver.
As TAD says
"A perfectly balanced ECC83 / 12AX7 will allow the tube output stage to perform at its optimum for smooth tone and definition. The overall responsiveness will be significantly improved by revealing the full dynamic headroom of the amplifier. Tight deep bass, complex lively mids and silky top end with overall definition.
When driven to saturation a guitar amp using a TAD ECC83 BALANCED PHASE DRIVER tube will provide its optimum sustain and sounds with harmonic overdrive.
With HiFi audio amplifiers it will tighten up tone and improve the soundstage to its max with given setup. Even in case of driving the output stage slightly into saturation, it will provide pleasing harmonic overtones underlining a tube amps signature tone quality when using our perefctly balanced phas driver tube selection.

Special selection BALANCED PHASE DRIVER tube for the use in phase driver / phase inverter circuits of guitar amps as well as for HiFi-Audio amplifiers."

 

[PelliX]

That's actually a fun little tester that the guy designed, hehe. Not the most versatile or precise of instruments depending on how you construct it, but fun nonetheless.

A tired valve needs some seconds to show max current on each triode.

Come again? The time it takes the heater filament to reach operating temperature has nothing to do with the performance of the valve.

I can see If valve heater it's ok. When filament is consuming about 150mA I know valve it's hot to work. I have one it's using 350mA all time. This valve don't works.

You could measure the resistance which will tell you if it's a short or open circuit. Current consumption is simply part of the spec of that given valve. Example:

230Vca

As Pete pointed out, you mean VAC here. There seems to be quite a bit of confusion about these matters. Although not everyone agrees on them, here are a few common examples;

Vpp: peak-to-peak voltage, AC of course.
Vp: peak voltage, AC again.
Vc, Ve, Vb: the voltage at the collector, emitter and base of a transistor, respectively. The same goes for FETs:
Vs, Vd, Vg: the voltage at the source, drain and gate of a FET.
Vcc: the voltage at the collector of a transistor, but often used for the DC input of low voltage circuits. Microcontroller or chip based circuits often use this as they are transistor based.
Vf: forward voltage drop of a component such as a diode.
VDC: DC voltage
VAC: AC voltage

As TAD says
"A perfectly balanced ECC83 / 12AX7 will allow the tube output stage to perform at its optimum for smooth tone and definition. The overall responsiveness will be significantly improved by revealing the full dynamic headroom of the amplifier. Tight deep bass, complex lively mids and silky top end with overall definition.
When driven to saturation a guitar amp using a TAD ECC83 BALANCED PHASE DRIVER tube will provide its optimum sustain and sounds with harmonic overdrive.
With HiFi audio amplifiers it will tighten up tone and improve the soundstage to its max with given setup. Even in case of driving the output stage slightly into saturation, it will provide pleasing harmonic overtones underlining a tube amps signature tone quality when using our perefctly balanced phas driver tube selection.

Special selection BALANCED PHASE DRIVER tube for the use in phase driver / phase inverter circuits of guitar amps as well as for HiFi-Audio amplifiers."

TAD are great at putting marketing lingo targeting audiophiles on their products. All that above is really, when you actually disect it, rubbish. Perfect balance based on the balance of the triodes in the valve without knowing the circuit in question is like guessing what the best size of screw for a purpose you do not yet know. As for the frequency response... well, show me a frequency response chart provided by the manufacturer?

 

[StingRay85]

Great stuff. I like my Maxi Preamp 2, but having a tester like this with multiple voltage and current readings is ever cooler. I should actually remeasure all my power tubes (300+), as a difference of 5% in mains voltage during the testing made a significant difference in the idle current. you should actually put a variac in front of it, and make sure to have a fixed set point for AC mains

 

[Kuga]

That's actually a fun little tester that the guy designed, hehe. Not the most versatile of precise or instruments depending on how you construct it, but fun nonetheless.



Come again? The time it takes the heater filament to reach operating temperature has nothing to do with the performance of the valve.



You could measure the resistance which will tell you if it's a short or open circuit. Current consumption is simply part of the spec of that given valve. Example:

View attachment 158075



As Pete pointed out, you mean VAC here. There seems to be quite a bit of confusion about these matters. Although not everyone agrees on them, here are a few common examples;

Vpp: peak-to-peak voltage, AC of course.
Vp: peak voltage, AC again.
Vc, Ve, Vb: the voltage at the collector, emitter and base of a transistor, respectively. The same goes for FETs:
Vs, Vd, Vg: the voltage at the source, drain and gate of a FET.
Vcc: the voltage at the collector of a transistor, but often used for the DC input of low voltage circuits. Microcontroller or chip based circuits often use this as they are transistor based.
Vf: forward voltage drop of a component such as a diode.
VDC: DC voltage
VAC: AC voltage



TAD are great at putting marketing lingo targeting audiophiles on their products. All that above is really, when you actually disect it, rubbish. Perfect balance based on the balance of the triodes in the valve without knowing the circuit in question is like guessing what the best size of screw for a purpose you do not yet know. As for the frequency response... well, show me a frequency response chart provided by the manufacturer?

You are useful to complain about the electrical nomenclature that I use, but not to contribute a circuit or idea to this easy/modest valve tester.

 

[StingRay85]