LAST update June 2013.

Click the pages you think might be interesting :-

AUDIO IDEAS FOR THE HOME.

Listening pleasure, class A, log sawing, class B, class AB, solid state history,

measurements, enough is enough,

NFB, triodes and NFB,

NFB and sales, circuit development, in house transformers,

future amps, preamps, SS amps,

NFB, tubes not bad, bandwidth, parts quality, tube choice, capacitors,

NOS tubes, testing tubes, add-ons, news groups.

VACUUM TUBE USE IN AUDIO AMPLIFIERS :-

TUBE OPERATION 1.

Basic tube operation, cathodes, anodes and grids, diodes,
triodes and pentodes.

Parameters of Ra, µ and gm.

Fig1. Schematic for a basic triode amplifier based on 6SN7.

DC flow for quiescent conditions, dc equilibrium,

Mutual effect of anode voltage and grid voltage on Ia electron
flow,

Effect of cathode bypassing biasing on Ra, and gain.

The tube modeled as a generator.

Fig 2. Schematic of basic 6SN7 generator model for illustrating
ac operation

of a tube.

NFB in the triode, AC signal flow, Cathode capacitor bypass
impedances,

tube gain formula, gain without capacitor bypassing.

Fig 3. Electrostatic effects in a 6SN7 triode.

NFB in the triode, how it reduces THD.

Fig 4. Electrostatic effects in the 6AU6 pentode,

pentode and beam tetrode operation, pentode Ra, µ and gm.

6AU6 triode connected and its amount of internal NFB.

NFB in 6SN7, and why ß = 1 / µ , with more NFB and
gain equations.

The Miller effect.

TUBE OPERATION 2.

Fig 5. Graph of 6SN7 Ra curves with load lines for 47k and 32k.

How to find Ra for a given working point and plot loadlines in
steps 1 to19.

Comment on THD and other topology outcomes.

Fig 6. Scanned Ra curves from Samuel Seely, 1958.

Explanations about the Ra curves. About gain with CCS load and
µ.

6SN7 THD with CCS load calculations from data curves.

TUBE OPERATION 3.

How negative feedback works.

Fig 7. Schematic for Basic NFB around an amplifier.

Explanations and formula for NFB gain reductions and effects of
NFB.

Fig 8. Schematic for Turner Audio 35 watt class AB triode amp
using KT90.

General notes about this amp which has the same overall gain and
NFB as the

basic example in Fig1.

Calculation method for output resistance with NFB.

The Model of the tube gain stage as a voltage generator.

Fig 9. Schematic of a power tube gain stage modeled as a
generator with

resistor to indicate Ra.

Explanations about the generator model.

Fig 10. Schematic of a tube gain stage using 6SN7.

Fig 11. Schematic of a tube amp drawn with each stage as a
generator with

loads and positions of shunt C to analyze the HF response and
graph all the

attenuation profiles.

A whole lot more about NFB, output resistance.

A simple formula for calculating output resistance of a real
amp.

More on stability of amplifiers with NFB and the use of RC
networks to

tailor open loop gain.

Fig 12. Graph of tube amp frequency response without global NFB
and

with global NFB, with no attempts to tailor open loop gain or
phase shift.

Fig 13. Graph of tube amp frequency response without and with
NFB

but with RC gain and phase shift tailoring

networks in place.

More about stability and NFB.

Critical damping methods for tube amps with NFB.

TUBE OPERATION 4

About NFB within triodes,

Testing a 6550 to measure Ra, Gm and µ.

Fig 1. Schematic A and B for testing 6550.

Schematics A and B explained,

How to determine Beam Tetrode and Triode Ra,

µ, and Gm.

Simple method to find Beam Tetrode and Triode Ra,

µ, and Gm.

Equivalent Model, Beam Tetrode, UL, Triode, 6550

Fig 2. Equivalent Model for calculation gain of UL connected
tubes.

Fig 3. Graph of Ra vs UL tap % for SE 6550.

SEUL 6550 and SEUL 6550 with CFB.

Fig 4. Schematics for SEUL and SEUL+CFB for 6550.

CFB with UL taps and without UL taps explained with maths.

TUBE OPERATION 5

About Input and Driver stages for PP tube amps.

Fig1. Schematic for basic input LTP.

Fig 2. Schematic for Driver LTP with balanced or un-balanced
inputs.

Fig 3. Schematic for Optimal LTP input and driver LTP for high
level operation.

All explained with many calculations and considerations.

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SE AMP OUTPUT STAGE
CONFIGURATIONS.

Content of this page is based
around schematics.

Fig 1. Three most used basic SE amp stages,
13W to 10W, SE pure tetrode,

SE Ultralinear, SE triode, 1 x KT88/6550.

Fig 2. 20W+ amp with SEUL with 2 x EL34, KT66,
KT88, KT90, KT120, etc.

Fig 3. The Equivalent Model of KT88 with g1
and g2 inputs treated as current

generators.

This allows understanding of
operating properties of a KT88, and its Ra, gm g1,

gm g2, and to analyze all voltages and currents in all electrodes to
determine

voltage gain, and effect of local NFB. The theory may be applied to all
power tubes

including pure triodes which do not have a screen, such as
300B and 2A3.

Fig 4. 20W+ amp with CFB, with 2 x EL34, KT66,
KT88, KT90, KT120, etc, using

same SEUL OPT in Fig 2.

Fig 5. 36W SE amp with CFB with 3 x KT88 etc,
using SEUL OPT, 25% UL tap,

1k3 : 5r6 Z ratio.

This was designed to include
"choke sink" for cathode current, and choke in anode

feed for driver tube.

Probably nobody has
ever built an amp like this because they need to source

good quality chokes.

The THD and Rout is much lower than conventional SEUL amps.

Fig 6. 25W PSEUL + CFB
amp designed around the Hammond 1640SEA output

transformer with mosfet CCS at KT88 cathodes,

Fig 7. 25W PSEUL + CFB amp designed
around the
Hammond 1640SEA output

transformer with choke at KT88 cathodes,

Fig
8. SE CFB output stage and SEUL output stages with
OPT with 3 windings.

Fig 9. Choke Feed SEUL
and SET output stages.

Fig 10. Choke Feed SET
amp with 845.

Fig 11. Choke Feed
SEUL with floating B+ supply.

Fig 12. Choke Feed SET
with floating B+ supply.

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PP OUTPUT STAGE
CONFIGURATIONS.

This page is about unusual
PP amps with seriesed output tubes in triode class A,

and for use of normal UL PP OPTs to obtain local Cathode
Feedback for much

greater linearity in the output stage.

Fig 1. Waveforms
of signal currents and 2H conventional PP Class A1 triode amp

with OPT with B+ at CT.

Fig 2. Waveforms
of signal currents and 2H in series connected class A1

triode amp with capacitor coupled OPT.

Fig 3. Complete
series triode amplifier with bootstrapped concertina

phase inverter/driver.

Fig 4. Complete
series triode amplifier with IST used for phase inverter /
driver.

Fig 5. Complete
unconventional UL amplifier which uses 40% screen taps to

provide local CFB from OPT.

Fig 6. Load line
for class A with 6550/KT88

Relevant notes and explanations about all.

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LOAD MATCHING 1. SE TRIODES.

Fig1. Anode resistance curves for GE6550A in triode from the
1950s.

Explanations of how the curves were obtained and what the curves
mean.

Fig 2. Schematic for testing power triodes.

Triode voltage generator model is included in explanations.

Fig 3. GE6550 triode curves with 2.5k RL and tangent to
calculate

Ra, µ and gm for any chosen working point.

Explanation of what load lines are.

How to plot LL graphically and read for gain, calculate power
output, and 2H distortion.

Fig 4. Measured Po vs distortion for 3 load values used with
EH6550 in triode.

Fig 5. Measured Po vs distortion for 3 load values used with
GE6550A in triode.

Fig 6. Measured Po vs distortion for 3 load values used with
KT88 JJ-Tesla in triode.

Fig 7. Measured Po vs distortion for 3 load values used with
KT90EH in triode.

Fig 8. My corrected Ra curves for EH6550 in triode with 3 values
of RL plotted.

Comments on loads recommended for EH6550 in triode.

Fig 9. My curves for EH6550 in triode without LL so you can
download them for use.

Fig 10. Ra curves for 300B measured after 1990 with 4.5k
loadline details.

Comparison of THD with beam tetrodes strapped as triodes.

Fig 11. Ra curves for GE6550 triode measured after 1990 with
4.5k load line details.

List of conclusions about beam tetrodes used as SE triodes.

Fig 12. Intermodulation test rig schematic for measurement.

Fig 13. Measuring the intermodulation distortion using an
oscilloscope wave form.

Comments about THD and IMD significance.

LOAD MATCHING 2. SE
BEAM TETRODES and PENTODES.

This page has the following content :-

Operation of the beam tetrode with cut-away sketch by RCA.

Fig1. Graph of Ra curves for GE 6550A beam tetrode with screen
supply = +350V.

Fig 2. Graph of Ra curves for GE 6550A beam tetrode with screen
voltage = +350V

plus 3 load lines and calculated results for gain, power output
and second harmonic

distortion.

Fig 3. Graph of Ra curves for GE6550A beam tetrode but with
screen supply = +200V.

Fig 4. Graph of Ra curves for GE6550A with one load line for
3.5k and calculated

gain, power and 2H.

Explanation of the effects of NFB application for 6550 beam
tetrodes.

Formulas for NFB and output resistance.

Fig 5. Graph for power output for single 6550 beam tetrode vs
anode load value.

Choosing the OPT ratio.

Fig 6. Graph of 6550 Ra curves for 6550 in UL mode with 43%
screen taps.

Calculated gain, power output and 2H for 4 different load
values.

Data for Ra, µ and gm for UL and comment on the effects of
NFB

and distortion outcomes.

LOAD MATCHING 3. PP TRIODES.

A very brief history of triode use. Class A Push Pull
operation basics.

Fig 1. Schematic of basic PP triode output stage with
current waveforms to explain

2H cancellations.

Comments on class AB1 amps, Williamson's amp, Class AB
efficiency, preferences,

Class AB1 basics.

Fig 2. Graph of EH6550 triode curves with load lines
for 5k a-a.

Minimum load for PP triode AB amps, Class AB1 operation
explained.

How to plot a load line to give the outcome for class AB
triodes,

Anode heat dissipation, Comment on B+ regulation, Biasing the
class AB PP stage,

Distortion, Output resistance, Negative feedback.

Using a higher RL value.

Fig 3. Graph for PP 6550 triode class AB1 power output vs RL
values.

Class AB power and portion of class A power listed for 8k : 6
ohms loading.

Fig 4. Schematic for 35 watt class AB1 PP triode amp with
KT90.

Speaker SPLs with 25 watts. Output transformer ratios.

Comment on using KT90 or multiple tubes.

LOAD MATCHING 4. PP BEAM
TETRODES.

Beam tetrode background,

Fig 1. Loadline graph for PP beam tetrode 6550 with 4k a-a load.

Plotting loadlines for PP tetrodes, 17 steps to find maximum
class AB power,

class A power.

Heat dissipation considerations and measurement, 92 watt Class
AB power

with Ea = 600V.

Biasing the output tubes, Distortion, Output resistance.

Using a higher RL such as 8ka-a,

Global NFB, its effect on output resistance, Calculation of
amount of applied NFB

and the output resistance with applied NFB.

Fig 2. Graph of power out vs RL .

Loading the PP beam tetrode output stage, OPT ratios.

Ultralinear and other output tube configurations, Driver
amplifier comments.

How to match loads to power tubes, load matching to 6550 &
KT88

and to some other beam tetrodes, pentodes and triodes.

-----------------------------------------------------------------------------------------

LOAD MATCHING 5.
About KT120, KT90, KT88, 6550.

OTL AMPS, PROS AND CONS.

This page is about :-

OTL amps, strengths and weaknesses, why OTL is so flawed.

Improving OTL performance, 1 to 6.

Table 1, Helps to explain use of mains toroidal PT as a speaker matching transformer.

Notes about Toroidal PT use.

Fig 1. Using a pair of 6AS7, loadlines for 4r, 8r, 16r, 32r, 64r - and what happens.

Calculating Pda for any level of operation.

Fig 2. Graph for Pda when using 4r to 64r loads.

Fig 3. Loadlines for class A1 with 6AS7.

Notes on class A1 use of 6AS7 - with OPT.

Table 2. Loading for class A1 using various numbers of pairs of output tubes.

Fig 4. Use of Class AB1 operation with 6AS7

Table 3. Use of 6AS7 with a "normal" PP OPT for class AB1 operation.

Table 4. Use of 6AS7 in Series Connection and with OPT for PP AB1 operation.

Use of 6C33c, notes.

Fig 5. Loadlines for 4r using 6C33c, Class B1, with Ea = +80V and +150V.

Discussions on peak tube current ability of 6C33c.

Fig 6. Class A1 operation and loadlines for 6C33c.

Table 5. Class A1 loading for various Ea and Ia and for Pda at idle = 40Watts.

Table 6. Configurations and output loads for a pair of 6C33c.

Fig 7. Understanding Class B1 loadlines for 6C33c.

Fig 8. Understanding Class AB1 operation of 6C33c.

Fig 9. Three basic ways for PP output tubes to be configured.

Fig 10. Schematic 30W class AB1 amp, 6CG7, EL34, IST, 6C33c Series Connected, + OPT.

Fig 11. Schematic 28W class AB1 amp, 2 x 6CG7, EL34, 6C33c Series Connected, + OPT.

Fig 12. Schematic 28W class AB1 amp, 6CG7, 2 x EL84, Technics FB circuit, 6C33c Series Connected, + OPT.

Fig 13. Schematic 30W class AB1 amp, 6DJ8, 2 x EL84, 6C33c, Normal PP OPT.

Fig 14. Schematic 30W class AB1 amp, 6DJ8, 2 x EL84, 6C33c, Circlotron PP OPT.

Class A1 SET with 6C33c.

Fig 15. Loadlines for class A1 with 6C33c SET.

Fig 16. Schematic 29W Class A1 SET amp, 6DJ8, EL34, 2 x 6C33c parallel + air gapped OPT.

Fig 17. Schematic 29W Class A1 SET amp, 6CG7, EL34 with g2 FB, 2 x 6C33c parallel

+ air gapped OPT with 50% CFB.

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OUTPUT TRANSFORMER THEORY.

Function of the output transformer, ( OPT ). How the OPT works.

Impedance and resistance transformation.

Fig1. Equivalent model of Ultralinear output stage tubes
and OPT.

Functions in the model and preferred OPT characteristics.

Test conditions for specifying OPT performance. Description of
OPT No1,

wire and turns and insulation description.

Fig 2. Cross section of bobbin winding details.

Fig 3. Schematic of OPT No1 when used in UL with two
impedance

matching settings shown.

Fig 4. Schematic of OPT No1 when used with 12.5% CFB
windings

and with two impedance matching settings shown.

Notes re recommended amounts of CFB to be used. Impedance
matching notes.

Table 1. Impedance matching available with OPT No1.

Table 2. Recommended output tubes for OPT No1 with winding
losses.

Comments about alternative tubes used with OPT No1.

Specification for OPT No1, notes re LF behavior, power handling
ability,

HF behavior, HF resonances, and distortion. Description of PP
OPT No2.

Description of SE OPT No3. Brief note about SE OPT No4.

-----------------------------------------------------------------------------------------------------------------

PUSH PULL OUTPUT
TRANSFORMER CALCULATIONS.

There are 5 pages covering this subject.

PP OPT Calc Page 1 :-

Contents, Brief reference to Radiotron Designer's
Handbook, 4th Ed, 1955.

Some general notes.

Design steps 1 to 34 for 2 x 6550/KT88/KT90, for TETRODES and PENTODES.

Design example is for OPT-1A
for up to 75Watts of audio power between 14Hz and 65kHz.

Loadline analysis, waveforms, metric wire size table, bobbin
winding diagrams, blank

sheets you may use.

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PP OPT Calc Page 2
:-

Design of OPT-1A continued....

Design steps 14 to 29 for 2 x 6550/KT88/KT90, for TETRODES and PENTODES.

Many drawings,
explanations, calculations etc.

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PP OPT Calc Page 3:-

Design of OPT-1A continued...

Design steps 30 to 46 for 2 x 6550/KT88/KT90, for TETRODES and PENTODES.

Many drawings, explanations, calculations etc.

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PP OPT Calc Page 4 :-

TAPPED SECONDARY WINDINGS for OPT-1ATS.

Design steps 47 to 53 for 2 x 6550/KT88/KT90, for TETRODES and PENTODES.

Many drawings,
explanations, calculations etc.

---------------------------------------------------------------------------------------------------------------------

PP OPT Calc Page 5 :-

FOR PP TRIODE CLASS A1
AND AB1, OPT-2A

Design steps 55 to
63, then 14T to 29T for 2 x 6550/KT88/KT90, TRIODE CONNECTED.

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SPEAKER MATCHING
TRANSFORMERS

This page is about speaker matching transformers.

Fig 1 to 13 show details of transformers and all is explained.

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ANODE DISSIPATION page
1 :-

This page still being
written 2014...

Calculations of anode heat
dissipation for class AB and B amps with OPTs.

Many graphs and explanations and formulas etc.

---------------------------------------------------------------------------------------------------------------------

ANODE DISSIPATION
Page 2 :-

This page still being written 2014...

Calculations of tube or solid-state device heat dissipation for
low bias Class AB

or Class B amps WITHOUT OUTPUT TRANSFORMERS aka OTL amps

with 6C33C or 6AS7G.

Graphs and calculation examples, etc.

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SINGLE ENDED OUTPUT TRANSFORMER
CALCULATIONS.

There are now 3 pages for this subject.

SE OPT Calculations Page 1.

Notes on RDH4, SE amp history, trends and preferences.

For operating conditions of common tubes.

Table 1. SE Pentodes, Beam Tetrodes, CFB, UL,

Table 2. SE Triodes.

Interpreting Table 1 and Table 2.

Design example for SE OPT4 with EL34.

Steps 1 to 30 with many diagrams, tables, and calculations.

Blank sheets for drawing response curves.

-----------------------------------------------------------------------------------------------------------

SE OPT Calculations Page 2.

SE OPT4 design continued,

Steps 31 to 44 with many diagrams, tables, and calculations.

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SE OPT Calculations Page 3.

Practical Testing of 8 Watt SEUL OPT for 1 x EL34 for old AM
radio.

Fig 19. Schematic for rather good 8 Watt SE amp, notes, old
radio picture.

Oscilloscope pictures of waveforms produced with 8 Watt SEUL
OPT.

SE OPT Easy Method for calculating any SE OPT, for Basic Parameters only.

Steps 1E to 10E.

High Voltage testing of transformers, test schematic, OPT3
details.

--------------------------------------------------------------------------------------------------------------

SE OPT for 1 x 13E1
, 25W, or for multiple parallel octal tubes.

Design flow for a couple of 25W SE OPT to suit 1 x 13E1 or 3 or

4 KT88/6550/KT90/300B or 4 x EL34, 5881, 6L6GC, 807.

Fig 1. OPT5 for SE 1.8k : 5 ohms with 44T x 50S core, all
details.

Fig 2. OPT6 for SE 1.8k : 2 to 14 ohms with 51T x 51S core, all
details.

Metric winding wire size chart for grade 2 polyester-imide wire.

-------------------------------------------------------------------------------------------------------------

WINDING OUTPUT TRANSFORMERS.

Practical winding methods and
description.

What you need to consider if
wanting to wind an OPT for yourself.

Image 1.
Bobbin winding details for OPT No1 mentioned in OPT
theory.

Image 2. Four
transformers on a work bench.

Image 3. Two 300w OPT
on bench.

Image 4. 500w OPT
on table.

Image 5. Winding
lathe with bobbin being wound.

Image 6. Wound
bobbin close up.

Image 7.
Close up of 300w OPT handmade bobbins on bench.

Winding procedure,
varnishing, alternative to varnish is applying Estapol 7008.

Metric winding wire size
chart for grade 2 polyester-imide wire.

------------------------------------------------------------------------------------------------------------------

TUBE AMP POWER SUPPLIES.

Definition of linear power supplies.

Fig 1. Basic wave forms in rectifier circuits.

Single phase house wiring, ac waveform basics, filling the bath
with water,

diode resistance, ripple voltage vs C vs Idc.

Cap ripple current and voltage ratings, ac to dc conversion
ratios, doubler rectifiers.

Fig 2. Schematic of 8585 amp power supply used as example for PS
calculations.

Minimum C value for reservoir C1 input cap, C reactance, Ripple
voltage calcs,

peak charge currents, charge current limiting, CRC and CLC
filters,

R and choke values, LC resonance, choke reactance, LC damping
resistance,

CT cap values, need for chokes. DC heater supplies, B+
regulators.

CRCRC and CLCLC filters.

Fig 3. Schematic for solid state regulator for screen supplies
in 300 watt amp.

Send me your SMPS schematics for B+ supplies.

-------------------------------------------------------------------------------------------------------------

POWER
TRANSFORMERS AND CHOKES.

About power transformer design and choke design,

I have refurbished the 2006 page and created a sub page solely
for chokes.

Due to demand for information about power transformer
and choke design,

there are 3 pages about chokes :-

Chokes
1 about basic chokes, testing chokes and for CLC PSU
filters.

Chokes 2 about Filter chokes
for "choke input" or LC filters in power supplies.

Chokes 3 about Chokes for DC anode feed.

---------------------------------------------------------------------------------------------------------------------

POWER SUPPLY FOR
TESTING TUBES.

Here is a rugged PSU design with HV rated bjts for adjustable
regulated B+ voltages

from +126Vdc to +585Vdc for up to 500mAdc output, and short
circuit proofed.

--------------------------------------------------------------------------------------------------------------------

RADIO
RE-ENGINEERING

Several examples of radical re makes of old radios with serious
quality problems.

Many pictures, some schematics.

---------------------------------------------------------------------------------------------------------------------

TURNER AM-FM
TUNER.

A totally tubed radio tuner including tubed multiplex decoder.

Schematics, notes, and an image.

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THD MEASUREMENT.

Sheet 1, Block diagram of THD measurement of amplifier,

Sheet 2, Wien Bridge oscillator, 1kHz, 0.004% thd,

Sheet 3, Attenuator and buffer and filter after 1kHz oscillator,

Sheet 4, L&C Bridged T notch filter for nulling 1kHz, THD
amp and filters.

Sheet 5, Hi Zin buffer for use with hi Z source to be tested.

Sheet 6, Front panel for THD testing unit.

----------------------------------------------------------------------------------------------------------------------------

AMPLIFIER FREQUENCY
RESPONSE TESTING

Listed test gear needed for testing amps,

Graph 1, blank sheet for use to plot response graphs.

Fig 1, Wien bridge sine wave oscillator with op-amp and switched
F.

Fig 2. Square wave oscillator with switched F and bjt amp.

Fig 3, Wien bridge sine wave oscillator with bjts amp.

----------------------------------------------------------------------------------------------------------------------------

WIEN BRIDGE OSCILLATOR.

6 decade frequency ranges, 1Hz to 1MHz, with square waves.

There are 3 schematics :-

Fig 1 shows the switched
R & C positive FB network and the simplified amp schematic
with output attenuator

and the negative FB network with j-fet to vary the amount of
NFB.

Fig 2 shows the full
details of the amp using discrete j-fets and bjts which gave
wider BW than most common op-amps.

Fig 3 Gives basic
properties of the Wien Bridge network.

Fig 4 shows the Schmitt
Trigger square wave schematic.

Full descriptions of schematics and expected problems DIYers and
dummies will face

-------------------------------------------------------------------------------------------------------------------------

WIEN BRIDGE
OSCILLATOR WITH TUBES.

This page is about Wien bridge oscillators using
vacuum tubes and some solid state for square waves.

Fig1, Wien bridge oscillator, tubed, from 2005. 1Hz to 220kHz

Fig 2,
Wien bridge oscillator, tubed, SHEET 1, amp, 2013. 1Hz to 2MHz

Fig 3, Wien bridge oscillator, tubed, SHEET 2,
buffer, output.

Fig 4, Wien bridge oscillator, tubed, SHEET 3,
Schmitt trigger and amp.

Graph 1, Square wave harmonic content.

Fig 5, Wien bridge oscillator, tubed, SHEET 4,
Power supply.

Fig 6, Small signal bjt discrete bjt op-amp.

-------------------------------------------------------------------------------------------------------------------------

MISCELLANEOUS SCHEMATICS
1.

1010w Integrated
amp
One channel shown with 2 x 6GW8, UL, classAB

Two triode phono stage NFB
eq
1 x 12AX7, feedback RIAA eq

Three triode phono stage NFB
eq
1 x 12AX7, feedback RIAA eq, buffer

Three triode phono stage Passive
eq
1.5 x 12AX7, passive RIAA, buffer

Phono Amp PSU
Schematic
Low-power supply for 2 and 3 tube preamps

10 tube Preamp April
2000
5 x twin triodes per channel

1 x j-fet 2SK369 simple
pre-preamp
A test circuit showing THD for a single 2SK369 j-fet

Test filter, Reverse RIAA
eq
A simple test filter with discrete RC components

MISCELLANEOUS SCHEMATICS
2.

Basic Balanced Shunt
FB
2 x 6L6GC

Balanced Shunt FB 100W
4 x 6550
per channel

Automatic servo bias
control
1 x KT88 etc.

Error correction standard UL amp
2 x KT88 etc.

Error correction fully balanced
2 x KT88 etc.

Simple line preamps 1 and
2.
2 triodes.

Simple line preamps 3, 4 and 5.
2 and 3 triodes.

Line preamp with switched gain and CCS 2
triodes.

Should you have any indispensable wisdom you'd like to have added then email me.

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