From: "Saved by Internet Explorer 11" Subject: RAT Tube Tester Project, By Steve Bench Date: Wed, 11 Feb 2015 11:40:13 -0800 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01D045EF.7F786000" X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.17609 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01D045EF.7F786000 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Content-Location: http://triodeel.com/tester.htm RAT Tube Tester Project, By Steve Bench =20

Back to Other Triode=20 Pages

rec.audio.tubes tube tester = project, by Steve Bench

Click here for = updated Schematic

Click on here for a = variable=20 voltage filament supply to accomodate odd voltage power triodes = (2A3,=20 300B, 50, etc.)

Background:

There are 3 fundamental Vacuum Tube (Valve) constants. These are transconductance (gm), plate resistance (rp) and mu. For tetrode and/or = pentode devices, mu is not significant, since the plate resistance is usually = much higher than the load resistance. There is a simple relationship between = these: mu =3D gm * rp. In a triode, the mu is substantially geometric factor, = so it does=20 not change much as the tube ages. Rather, the gm decreases with time = and the rp increases. Therefore, a measure of the goodness of a tube is generally = related=20 to its measured gm. This is done in a "transconductance" tube tester, = but, as=20 the specific voltage and current used in a particular application is not possible or practical to set up, this limits the usefulness of the = traditional tube tester. The purpose of the described device is to circumvent these limitations, and allow evaluation of tubes under operating conditions = really used in your specific application.

DEFINITIONS:

Transconductance:

This is defined as the incremental change in plate current for an = incremental=20 change in grid voltage, with all other parameters (plate voltage, for = example)=20 held constant. The way this is done is to place a small AC voltage (lets = say 100=20 mV) on the grid and measure the output AC current on the plate. In = practice,=20 this is done by measuring the voltage across a small resistor, (lets say = 100=20 ohms) connected from plate to a constant DC voltage source. The current = can be=20 controlled by placing a constant current source in the cathode circuit = of the=20 tube under test, and bypass the cathode for AC purposes. For the = example given=20 (100 mV AC on the grid, and a 100 ohm plate "current sensing" resistor), = a=20 transconductance of 1 mS (1000 micro mhos) would be indicated as a 10 mV = signal=20 across the 100 ohm resistor.

Mu:

This is defined as the incremental change in plate voltage for an = incremental=20 change in grid voltage, with all other parameters (plate current, for = example)=20 held constant. The way this is done is to place a small AC voltage (lets = say 100=20 mV) on the grid and measure the resulting AC voltage on the plate, with = the=20 plate connected to a high impedance load (current source). For the = example=20 given, (100 mV AC on the grid), a mu of 20 would be indicated as a 2 = volt signal=20 at the plate. Note: The "resistance" of the constant current load must = be=20 substantially higher than the plate resistance of the tube under test = for the=20 results to be accurate. Plate resistance: This is defined as the = incremental=20 change in plate voltage for an incremental change in plate current with = all=20 other parameters held constant. This is not directly measured in the = proposed=20 project (at least initially) but is calculated by the formula rp =3D = mu/gm.

SYSTEM BLOCKS:

Sources:

1. Filament Voltage: Initially fixed at 6.3VAC (no grumbling, we'll = =20 "improve" on this over time). This supply is referenced to about = 40VDC to=20 allow realistic confirmation of (no) heater to cathode leakage or = shorts.=20

2. Plate (anode) Voltage: Lets say 300 VDC, at 50 mA max. Initially = this =20 will be allowed to vary from about 40 volts to about 300 volts, = controlled=20 by a small potentiometer operating a regulated supply. The 50 mA = allows both small signal and power tubes to be measured. This supply is current = limited at 50 or so mA, to handle the defective "shorted tube" case.

3. Screen Voltage: Same as #2, independently controlled. 4. Plate = current: Actually a part of plate voltage control. This is operable only in = "mu" mode=20 to provide a high impedance load as indicated above. The actual tube = current=20 is controlled by the cathode current sink (see below), and this is = adjusted=20 for the test condition voltage.

4. AC: 100 mV sine wave at about 1 kHz. This source is protected = against grid to plate or grid to cathode shorts.

Sinks:

1. Cathode current: Variable from about 100 microamps to 50 mA via = a potentiometer controlling a constant current circuit. This allows = gm/mu to=20 be measured at any desired current level. Combined with the variable = plate voltage source, gm/mu can be measured over a range of voltage and = current. This sink is tied to a negative (about) 60 volt source, to simulate = bias conditions to about -60 volts, primarily for testing of power tubes. = Notice that the actual voltage applied to the tube will therefore be up to = about 360 volts.

Controls:

1. (S1) On/Off.

2. (S2) gm/mu switch.

3. (S3) Side1/Side2 switch for switching between "halves" of dual = triodes.=20

4. (S4) Triode/Pentode switch to allow "triode connection" of = pentodes.

5. (VR1) Plate voltage control.

6. (VR2) Plate current voltage adjust (mu mode).

7. (VR3) Tube current control.

8. (VR4) Screen voltage control (tetrode/pentodes only).

Indicators:

1. 2 jacks for DMM connection. The DMM measures AC voltage in gm = mode, and=20 DC plate voltage and AC voltage in mu mode.

2. Green Power LED.

3. Yellow LED that illuminates if grid is driven positive.

4. Red LED that illuminates on H-K leakage or short.

5. Red LED that illuminates on high current (plate etc shorted).

Sockets:

1. Octal: (7AC/7S/8EP) Handles KT66/EL34/6L6/6550/6V6-GT (pins = 1&8 connected together).

(Uncle Ned notes: 7027 would require disconnecting Pin 1 from Pin 8. 6BG6-G/GA and 6CD6-G/GA/7867 by adding a plate/anode cap. Possibly = 6B4-G could be accomdated too...)

2. Octal: (8BD) Handles 6BL7/6SN7/6SL7/6AS7/6080/6336/6528 etc.

3. 9 pin: (9A) Handles 12AT7/AU7/AX7/ECC81-3/12BH7 etc.

4. 9 pin: (9AJ/9DE) Handles 6DJ8/6BK7/BQ7/BZ7/6CG7/6922 etc.

5. 9 pin: (9V) Handles 417/5842

6. 9 pin: (9BF) Handles 12BY7/12GN7/ etc.

7. 9 pin: (9CV) Handles 6BQ5/6CW5/7189/El84 etc.

8. 7 pin: (7BK/7CM) Handles 6AU6/6AH6/6GM6 etc (pins 2&7 = connected together).

OPERATION:

gm test:

Procedure:

Plug the tube into the appropriate socket, set the gm/mu switch to = the gm position. Set the desired plate voltage and the desired current = level. Read the AC voltage on the DMM.

Reading GM 1 mV 100 umhos (0.1 mS) 10 mV

1000 umhos (1.0 mS) 100 mV 10000 umhos (10.0 mS) etc.

A "constant current" is fed into the cathode. This is bypassed for = the=20 transconductance measurement. This allows the grid-cathode voltage to be established by the tube itself. There is a warning LED to indicate that = the desired current has caused the grid to go into grid conduction region. = This constant current is one of the "variables" that we can use to evaluate = the tube=20 under test, so that gm can be plotted vs current. A constant voltage is = set onto=20 the plate, and this is the other "variable" we can use to evaluate the = tube=20 under test. A 100 mV AC signal is applied to the grid, and the gm is = found by=20 measuring the AC voltage produced across a 100 ohm sampling resistor. = mu test:=20 Procedure: Plug the tube into the appropriate socket, set the gm/mu = switch to=20 the mu position. This test is only going to work with triodes. Set the = desired=20 level, and adjust the "plate current voltage adjust" to the desired = plate=20 voltage level by reading the DC voltage with the DMM. Then switch the = DMM to=20 AC voltage and read the AC voltage on the DMM.

Reading MU

100 mV 1 V

1.0 V 10

10.0 V 100 etc.

A "constant current" is fed to the cathode. This is bypassed for AC = purposes=20 to allow the mu measurement. This allows the grid-cathode voltage to be=20 established by the tube itself. There is a warning LED to indicate that = the desired current has caused the grid to go into grid conduction region. = This constant current is one of the "variables" that we can use to evaluate = the tube=20 under test, so mu can be plotted vs current. The plate voltage is = established=20 via a quasi-constant current source whose output resistance is much = higher than=20 the plate resistance of the tube, allowing an accurate mu measurement. = This=20 allows plate voltage to be varied, so that mu may be plotted against = plate=20 voltage. The mu is found by simply measuring the AC voltage on the = plate.

CIRCUIT DESCRIPTION

The power supply uses 2 12.6VCT transformers connected back to back. = This is used for the 6.3V for the filaments then provides an isolated (about) = 105-110 volts AC. Two DC voltages are developed. The first is a voltage tripler = to give back a loaded voltage of about 330VDC (With no tube load, it provides = about 400 volts). This wimpy approach was taken purposely to minimize heat = loading on the "guts" of the circuit under abnormal (shorted tube) conditions. A 2.2 = mA=20 constant current source drives a set of zener diodes, to establish a = constant voltage reference of about 306 volts. This is fed to 2 separate VFET = "source follower" regulators. The gates are simply fed with pots refered to the regulated voltage. Each regulator is also current limited. The second = main supply is a negative half wave rectified supply that provides 60 to 100 = volts (depending on load current) for the constant current source that drives = the cathode(s). The negative supply has a fairly healthy 20 mA bleeder on = it. In=20 the bleeder string is a 10 volt zener used to provide a voltage = reference for=20 the current source, and a 5.1V zener sitting on the ground side. This is = used to drive a CMOS 1 kHz oscillator.Each regulator is current limited by a = simple transistor "starving" the gate of the source follower. The 22 ohm = "sampling" resistor causes current limit to occur at about 25 mA. This resistor = may be altered if desired. The plate side is limited at 55 mA by using a 10 = ohm resistor. The main tube current source uses a 10 volt zener to = establish a constant gate voltage, adjustable from about 2.5 to about 10 volts. = This causes the 133 ohm resistor in the FET source to provide a constant current of = about 0.1 mA to about 50 mA.

A word of caution on the FETs. Make sure the resistor that's = in series=20 with the gate lead is AT THE FET. This prevents the critters from = oscillating at=20 some VERY high frequency. Also, note that although these parts are = rugged IN THE=20 CIRCUIT, they can be blown by static charge while assembling the = circuit.

The 1 kHz oscillator is a schmitt trigger oscillator. The "triangle" = is fed=20 through another part of the inverter package, which rounds it a bit more = and=20 then filtered and divided to 100 mV. This produces a relatively pure = sine wave=20 with less than 1k source impedance.

The 6.3VAC is referenced to 51VDC via a 47k resistor and a LED. This = provides=20 indication of heater to cathode leakage or short. Using "universal" = 120-240=20 transformers allows easy build by anyone. Note that the second = transformer is=20 powered from the first one (the 12 volt windings are coupled together) = and the=20 high voltage produced is always wired 120V.

Note however, the first transformer should be wired for either 120 = or 240 depending on your high tension source.

CALIBRATION:

After conpleting the unit and finding the 4 or 5 things you did = wrong, you should be pleasantly suprised by the green LED ON.

With NO tubes installed, the following voltages should be present: =

Point Voltage Notes
A 420VDC 380 to 430 volts is OK
B 306VDC 296 to 316 volts is OK
C ----------------->>> This will vary from 0 to 300 volts depending on = VR1.=20 If you set this to about 200 volts, then measure current to = ground,=20 you should see about 55 mA (50-65).
D ------------------>>> This will vary from 0 to 300 volts depending on = VR3.=20 If you set this to about 200 volts, then measure current to = ground,=20 you should see about 25 mA (20-30).
E -100V -80 to -110 volts is OK. This is the current = source=20 output.
F -110VDC -85 to -120 is OK.
G -100VDC Should be 10 volts more positive than = F.
H -4.6VDC Yeah, I know its a 5.1V zener. Trust = me.
J ------->>>> This will vary form 0 to about 250 mV AC rms 1 = kHz.=20 The frequency ought to be within 200 Hz of 1kHz. Level is = controlled=20 by VR4.

Calibrate Plate Voltage (VR1):

With a voltmeter connected to point C, calibrate VR1. This will be = linear taper. I find I can make minor "ticks" every 10 volts, major ticks = every 50=20 volts from 0 to 300 volts. Since there is no "load" on this point, you = could=20 temporarily place a 100k resistor to ground to provide some load to make = the=20 calibration more accurate.

Calibrate Screen Voltage (VR3):

Same procedure as above. except point D and calibrating VR3.

Calibrate current source (VR2):

Connect a milliameter from point E to ground. You should start to see = current=20 flowing at about 20 degrees of rotation on VR2. If you have to go much = more=20 clockwise to see current flowing raise R15 (270k) to 330k or higher. If = you see=20 more than 100 uA flowing fully counterclockwise lower R15 to 220k or = lower. The=20 220k across the pot (R17) creates a somewhat log taper. I found I could = make minor ticks .1 mA to .5 mA, then 1 mA, then 1 mA ticks from 1 to 10 mA, = 2 mA ticks to 20 mA, and 5 mA ticks from 20 to 50 mA.

Set AC Level (VR4):

Connect an AC VM from point J to ground. Set the voltage to 103 mV = +/- 2 mV with no load otherwise attached. This will make the operating voltage = very nearly 100 mV across the range of currents and voltages. Thats all = there is to the calibration.

PARTS LIST

Most of the parts are available from Digi-key or Mouser. The = exception is=20 the tube sockets, so you'll have to go to Triode.

I have not listed chassis, hardware, knobs, and the like. Use what = you like.=20 I used an old Lafayette (!) rip off of the old Ten-tec boxes that is = about 12"x8"x 6" or so. Also, sometimes there's a price break at a larger = quantity,=20 so feel free to order extras for another project. E.g., 1N4007 diodes. I = generally order 100 at a shot, you can use the extras by bending the end = of each=20 lead slightly. They are perfect for hanging ornaments on your (place = your=20 holiday here) tree. Ho Ho Ho!

Ed. Note: We have the = sockets=20 and most of the capacitors=20 (or higher voltage rating equivalents). There are, I'm pretty sure, = SK or=20 ECG equivalents for most of the diodes & transistors, if you want to = buy=20 them at local distributors.

QTY. DESC REF
6 100 uF 350V Elec. C1, C2, C3, C6, C7, C8
2 47 uF 450V Elec. C4, C5
1 47 uF 10V Elec or Tant. C9
2 .1 uF mylar, poly, etc. C10, C13
4 .01 500V+ C11, C14, C16, C17
1 1.0 uF 50V+ C12
1 .22 uF 50V + C15
9 1N4007 1A 1KV diodes CR1-7, CR18, CR19
1 Hi efficiency green LED CR8
6 51V 5% .5 watt zeners CR9-14
1 Hi efficiency red LED CR15
1 5.1V .5 watt 5% zener CR16
1 10V 1W 5% zener 1N4740 CR17
1 1A fuse-of sufficient voltage rating,ie: not an automotive fuse F1
1 fuseholder-depends on type of fuze used.
1 Linecord -- country dependent
1 dual binding post J1a,b
1 MPSA92 350v PNP TO-92 Q1
2 MPSA42 350v NPN TO-92 Q2, Q3
3 IRF820 TO220 VFET(you can substitute IRF820, 830, = 840 or=20 IRF710, 720, 730, 740) Q4, Q5, Q6
3 -- Heat sinks for the FETs Mouser p/n M532-569022B00 or equiv
12 470 ohm 1/4w 5% R1, R27-37
1 47k 1/4w 5% R2
1 100K 2W 5% R3
4 10k 1/4w 5% R4, R18-20, R23, R26
6 1M 1/4w 5% R5, R9, R22, R25
1 10 ohm 1/4w 5% R6
3 100 ohm 1/4w 5% R7, R8, R10
1 470k 1/2w 5% R11
1 22 ohm 1/4w 5% R12
1 200 ohm 2w 5% R13
1 3.3k 5W 5% R14
1 270k 1/4w 5% R15
1 133 ohm 1/2w 1% R16
1 220k 1/4w 5% R17
1 200k 1/4w 5% R21
1 160k 1/4w 5% R24
1 SPST switch S1
2 DPDT switch S2,S3
1 3 position switch S4
2 120/240v to 12.6VCT 40W mains transformer T1,T2
1 74HC04 (not HCT) U1
1 7 pin tube socket V1
2 Octal tube sockets V2,V3
5 9 pin tube sockets V4-V8
3 1 meg lin taper pot VR1, VR2, VR3
1 2 k trimmer pot VR4

Hi All, Modifications to the gm/mu Tester - Rev B

1. During checkout, I found one condition of plugging tubes = (sideways - one pin was broken and 2 others shorted) that I could cause the plate = regulator to break, so I've added two zeners to prevent that from happening in = the future.

2. Added a 4D 4 pin socket for 811's etc. This also adds a 5th = switch to=20 "short" heater to cathode.

3. A second schematic page is now available... this adds a = variable regulator to the filament source, to provide a variable filament = voltage=20 from 2.5 to 12.2 volts. This is not required for operation of the basic = tester,=20 but provides coverage for 2A3's, 50's etc. Add it if you like.

4. A "plate cap" is added to the schematic for testing things like = 811's,=20 and 6DQ6 and related 6AM socketed tubes in the 7AC socket.

5. There was one "unclear" portion on the schematic in the tube = socket=20 connections. This is clarified.

6. See below for settings to test a number of common tubes, so you = don't have to look them up.

Page 1 BOM (Bill Of Materials)Changes:

Qty Description Ref Designator
1 SPST Switch S5 Same as S1.
2 15V .5w Zener CR20, CR21 1N5235B
1 4 pin tube skt V9
1 Plate Cap

Page 2 BOM:

Qty Description Ref Designator
2 1000 uF 25V C101, C102
1 .01 uF disc C103
5 3A 40V Schottky diode CR101-CR105 1N5822
1 50 uH 5A inductor L101 (actually 68 uH)
2 2.2k 1/4W 5% R101, R102
1 Maxim MAX724 U101 Available from DigiKey
1 Heat Sink Same as on Pg 1
1 10k lin taper VR101

Page 2 Calibration Procedure:

With a DVM connected to the output going to the filaments, calibrate = VR5 at 2.5, 3, 5, 6, 6.3, 6.6, 7.5, 10, 12, 1.2 volts. Check this voltage with = a 50C5 (or 35W4 etc) plugged into the 7BK socket as a load. This voltage = should not substantially change with load. Regards, Steve

Steve's gm/mu Tester. "Standard" Readings for many Tubes.

Note: Vf is 6.3V unless otherwise indicated. To test other than 6.3V = tubes, you must build the Filament circuit shown in the schematics' second = page. For the 4D socketed parts, you must turn ON S5, which connects cathode and=20 filament. Note the shorted H-K LED will come ON in this case. P after = the socket=20 means use the plate cap to hook up the plate.

THIS LIST IS NOT INTENDED TO BE ALL INCLUSIVE! Many of the tubes not = listed here can be found in the GE Essential Characteristics book.

Vf=3DFilament voltage. Va=3D Plate or anode voltage. Vg2=3DScreen or = grid #2 voltage.Does not apply to triodes.Vg1=3DNegative grid voltage. Only = given for power triodes. Ik=3Dcathode current. gm=3Dtransconductance as expressed = in=20 micromhos (typical US designation,1000 umho is equal to 1 ma/V, 1 ma = change in=20 anode current for 1 volt chage in grid (g1) voltage). mu=3Damplification = factor.=20 Only given for small triodes.

Note that the gm and Ik given are for typical new tubes. = Depending on=20 the tube type, variations of 10 to 20% can be expected to be seen, = even for=20 unused tubes,generally the higher the Ik or gm, the wider the = variation that=20 one can expect. High gm tubes such as 6DJ8, 7308, 12GN7, etc, are often = factory=20 spec'd to as wide as a -20 +40% tolerance in gm. Others may show an = increase in=20 Ik after being "cooked" with plate current for awhile, so if your NOS = Mullard=20 12AX7's test too low, try running them for a while, then retest = them.

Tube Socket Vf Va Vg2 Vg1 Ik gm-umho mu
2A3 4D 2.5 300 -- -45 50 4200
6A3 4D 300 -- -45 50 4200
6AG5 7BK 250 150 8.5 5000
6AH6 7BK 300 150 12.5 9000
6AJ5 7BK 30 30 3.5 2300
6AK5 7BK 180 120 10 5100
6AQ8 9AJ 250 -- 10 5700 59
6AS6 7BK 120 120 9 3200
6AS7 8BD 150 -45 60 2000
6AU6 7BK 250 150 15 5200
6BA6 7BK 250 100 15 4400
6BC8 9AJ 150 10 6200 35
6BD6 7BK 250 100 12 2000
6BG6 7AC-p 250 250 75 6000
6BH6 7BK 250 150 10 4600
6BJ6 7BK 250 150 12 3600
6BK7 9AJ 150 18 8500 40
6BL7 8BD 250 40 7000 15
6BQ5/ EL84 9CV 250 250 45 10500
6BQ6 7AC -p 250 150 45 5200
6BQ7 9AJ 150 9 6000 35
6BS8 9AJ 150 10 7200 36
6BX7 8BD 250 42 7600 10
6BX8 9AJ 65 9 6700 25
6BZ6 7BK 125 125 18 8000
6BZ7 9AJ 150 10 6800 36
6BZ8 9AJ 125 10 8000 45
6CA7/ EL34 7AC 250 250 45 10000
6CB6 7BK 125 125 17 8000
6CD6 7AC-p 175 175 75 7700
6CG7 9AJ 250 9 2600 20
6CW5/EL86 9CV 170 170 45 10000
6DN7 (sec 1) 8BD 250 8 2500 22.5
(sec2) 250 41 7700 15
6DJ8/ ECC88 9AJ 90 15 12500 33
6EM7 (sec 1) 8BD 250 1.5 2200 66
(sec 2) 150 45 7000 5.4
6F6 7AC 250 250 40 2500
6GM8/ ECC86 9AJ 7 .9 2600 14
6JK6 7BK 125 125 15 18000
6K6 7AC 250 250 37 2300
6L6 7AC 250 250 45 5100
6SL7 8BD 250 2 1500 70
6SN7 8BD 250 9 2600 20
6V6 7AC 250 250 45 4100
10 4D 7.5 300 -20 20 1600 8
12AT7/ ECC81 9A 250 10 5500 60
12AU7/ECC82 9A 250 10 2200 17
12AV7 9A 150 18 8500 41
12AX7/ ECC83 9A 250 1.2 1600 95
12AY7 9A 250 3 1700 44
12BH7 9A 250 11 3100 16.5
12BY7 9BF 250 180 32 11000
12BZ7 9A 250 2.5 3200 98
12GN7 9BF 250 150 35 36000
12HG7 9BF 300 135 35 32000
50 4D 7.5 300 -45 20 3800
275A 4D 5.0 150 -40 17 1600 2.6
300B 4D 5.0 300 -61 60 5500 3.8
350B 7AC 300 250 80 7700
417A 9V 150 26 24000 43
811A 4D -p 300 30 1500 95
5751 9A 250 1 1200 70
5998 8BD 120 45 15000 5.4
6336 8BD 200 -45 185 11000 2.7
6528 8BD 110 45 30000 9
6550 7AC 275 275 45 10000
6922 9AJ 90 12 11500 33

6SU7 8BD see 6SL7

12AD7 9A see 12AX7

12AZ7 9A see 12AT7

12DF7 9A see 12AX7

12DM7 9A see 12AX7

12DT7 9A see 12AX7

12DW7 9A sec1 =3D 12AX7, sec2 =3D 12AU7

572 4D -p see 811A

5691 8BD see 6SL7

5692 8BD see 6SN7

5725 7BK see 6AS6

5749 7BK see 6BA6

5814 9A see 12AU7

5842 9V see 417A

5881 7AC see 6L6

5965 9A see 12AV7

6072 9A see 12AY7

6080 8BD see 6AS7

6113 8BD see 6SL7

6136 7BK see 6AU6

6188 8BD see 6SL7

6189 9A see 12AU7

6201 9A see 12AT7

6265 7BK see 6BH6

6485 7BK see 6AH6

6520 8BD see 6AS7

6660 7BK see 6BA6

6661 7BK see 6BH6

6662 7BK see 6BJ6

6679 9A see 12AT7

6680 9A see 12AU7

6681 9A see 12AX7

6851 9A see 5751

7025 9A see 12AX7

7189 9CV see 6BQ5

7247 9A sec1 =3D 12AX7, sec2 =3D 12AU7

7308/E188CC see 6922

7581 7AC see 6L6

7728 9A see 12AT7

7729 9A see 12AX7

7730 9A see 12AU7

7867 7AC-p see 6CD6

8431 9AJ see 6ES8

ECC81 9A see 12AT7

ECC82 9A see 12AU7

ECC83 9A see 12AX7

ECC88 9AJ see 6DJ8

E88CC 9AJ see 6922

EL34 7AC see 6CA7

EL84 9CV see 6BQ5

Back to Other Triode=20 Pages

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