Jaap Knoppert Tube amps for guitar

ZABS Submini PedalAmp

2011-12-03T02:45:00.000-08:00

Another experiment with submini tubes: 6112 as preamp tube and a 6021 in the poweramp. Preamp is a regular two stage preamp, normally biased, 22u bypass cap over the first stage and 470n over the second stage. Tone stack is a baxandall type. For the second stage I used a split plate resistor (22K/75K) to make sure there’s not too much signal going into the poweramp too early. I spent most of the time tweaking the poweramp. I started with a self split push pull. It sounded ok but then I tried a parallel SE configuration with a 6021 and that sounded better in my opinion. So that’s what it is now. For the psu I used a standard Nixie power supply unit, a dc/dc converter and that works fine. Power transformer secondary is 9 V @ 1.3 A. Followed by a bridge rectifier and a cap and than into the Nixie dc/dc converter. That results in a B+ of 175 V @ 11mA for the total amp. That’s just under the max of 12mA for the Nixie unit. No problems with heat or voltage dropping. Another bridge rectifier and a LM317 are used for the 6.3V filament.
Output: around 400mWatt, Class A.

Dimensions (inches): 9 x 5 x 2

Soundclip

ZABS Suitcase PP/SE

2011-05-29T14:57:00.000-07:00

Why hide your amp behind wood and tolex? The ZABS Suitcase has nothing to hide! My main goal for this project was to make an amp with a lot of sound possibilities. From clean to mean and suitable for different styles of music. Low volume and a unusual design and housing. Top cover is made of plexi glass. With a marker you can draw your own design or make notes for example about the setting of the amp for a song.

The Suitcase offers two channels and two different power amps. You can choose between a single ended 6V6 power amp in class A (2 Watt) or a push pull 6021 powerstage class AB (700 mW). The preamp uses 6112 submini triode tubes. Channel I has 2 gain stages. Channel II consists of 3 stages and has the option to swich in a bit or a lot more gain. Both channels have there own gain control.

After the preamp comes the cathode follower, treble, mid, bass tone stack and master volume. When the SE 6V6 power amp is used the signal goes from the master volume after the tone stack straight into the power tube. No overall negative feedback (nfb) is used in the SE power amp.

The PP 6021 amp has another gain stage after the master volume followed by a cathodyne phase inverter; a submini 6021 is used for both functions. Gain is tweaked with split plate resistors to avoid the small power tube to be overdriven too early and too much. The PP amp has features as Presence and Resonance in the nfb. Bias can be switched between catode and fixed bias for a more tight sound. B+ rail for the amp is around 190V.

It was great to experiment with the small submini tubes and combine them with a 6V6.

Dimensions (inches): 17 x 9 x 3

Sound samples: 1. SE clean channel 2. SE OD channel 3. SE OD channel xtra gain 4. PP amp

ZABS ECL86 SE

2009-11-05T14:58:00.000-08:00

Zabs yellow cab! A high gain amp with three preamp stages and a single ended power amp. As you can see the amp runs on only 2 tubes: a 12AX7 and a triode/pentode ECL86. The amp is based on the Hi Octane but it has a one knob tone control which acts like a sort of mid control. This gives the amp a sound range from Marshall to a sort of Vox like sound. I tried all kind of tone controls but this is my favourite for this amp. Also because it gives a bit more signal and overdrive to the power tube.
You can use just two preamp stages or all three. The third one can be switched in for more gain.
I used a one star grounding system and the amp is very silent. At first it hummed and oscillated but I found out that two things were crucial: 1. grounding the mid pin of the noval socket of the ECL86 (stopped the oscillation) and 2. the reference at the catode of the powertube for the filament (no more hum). The Siemens ECL 86 pentode runs at 260V into a 10K primary OT. Output about 3 Watt. The 12AX7 is by Tung-Sol, I like that tube very much.

Dimensions (inches): 12.2 (w) x 5.9 (h) x 4.3 (d)

Tremolo in a Fender Bassman

2009-01-16T13:47:00.000-08:00

I'm working on building in a tremolo into a Fender Bassman. Like in the Fender Vibroverb amp the trem is connected to the bias resistors of the output stage. At first it didn't work at all. With help from Joe Kerr and AX84 I found out that the bias of the output tubes is crucial. The Bassman is normally biased at around -45V at idle. But than the tremolo hardly had any effect. First I changed resistor *) to 100K instead of 470K and that helped a bit but not much. Later I biased the Bassman to -53V with the intensity pot at zero (bias is around -44 with intensity at max). That is the key! Listen to the sound clip for an impression. At the end of the clip you can hear a strong 'chop chop' sound. When I use a JJ Electronics tube (not in this clip) this sound is a bit less strong.
As you can see on the picture the tremolo is now ready. I use the tube from the Bass channel but everything is still there so the Bassman can be changed back to original. No new holes were necessary. The trem is working very good now; without any 'chop' sound. Volume switch is for on/off and Treble and Bass pots are for Speed and Intensity.

Sound clip 1 (No title No song Trem test; 6minutes: from no trem to max trem)

ZABS Champ Vibro XL

2008-10-19T08:36:00.000-07:00

The ZABS Champ XL has gone through some stages. This is the final result. The PSU rectifier tube is a EZ81 instead of the original 5YR3. There's a switch for normal filtering or extra filtering when using a 6L6. That tube draws more current than a 6V6 and the extra caps keep the amp quiet.
It started out as a 2 channel amp with an octal triode 6SL7 and the regular noval 12AX7. Normal Champ set up but with a Moonlight one knob tonestack. It sounded good but I was not totally happy with the tone stack and sound at higher volume. So after all I ended with the normal Champ blackface set up. Preamp stage 1, Fender tonestack, Volume, pre stage 2 and SE poweramp. Also tried it with a 6SJ7 pentode just like the Champ 5C1. That is a great sounding tube but after all I changed the amp again. So finally the preamp uses a 12AX7. And the amp now has a tremolo with a 6SL7 triode. So it has become a Champ Vibro XL!

Other possibilities:
NFB can be switched 'on', 'off' or 'on with presence' for different kind of dynamics and sounds. It’s possible to switch between catode resistors so you can use either a 6V6 or 6L6 power tube. The tonestack can be switched off for a gain boost in the preamp. Also the 'sound shape' of the tonestack can be changed with a switch giving the amp more mids in the sound.
So it’s not an exact Fender Champ and it's not something new either. Sounds ok though! The 6L6 GC and the other extras is why I added the XL to the name. Amp sounds great with Hytron Jan CHY 6V6 and a Philips 6L6WGB gives a sound somewhere between a 6V6 and 6L6. Great!

ZABS Blues PP 6G6

2008-02-11T12:16:00.000-08:00

The goal for this project was to make a good sounding amp for the range clean to edgy blues, rock. Like the ZABS Vintage this amp uses 6G6 pentode power tubes for low power. With 2 Watt you can turn the volume all the way up. The ZABS blues is based on a Fender DeLuxe; so the circuit has the classic line up: preamp stage 1 followed by the Fender tone stack and volume pot and than followed by preamp stage 2. But this ZABS amp has some special options. For the preamp the ZABS blues has two tubes available; a 12AY7 and a 12AX7. You don’t have to change tubes. For stage 1 you can either use the 12AY7 or the 12AX7. Or you can switch them in parallel. The second preamp stage can be mixed between 12AY7 and 12AX7. With a balance pot you’re able to dial in (more of) the AX7 or the AY7. This has an effect on the amount of signal that goes to the phase inverter. These options give the amp extra possibilities and subtle and very useful sound changes.

The long tail phase inverter uses a 12AT7. The push pull poweramp uses 6G6 pentodes. Overall NFB is on a switch providing 3 possibilities: no NFB, Fender like NFB or less than Fender NFB. For the power supply the amp has a specially made power transformer with several secondaries. One tap is used for the poweramp deliviring around 200 V for the plate of the power tubes. Another tap is used for the preamp and phase inverter (B + 300 V). The power supply uses a choke for the poweramp and the tubes are fixed biased in class AB. There’s a Sag switch which is nothing more than a 150 Ohm resistor in the power supply rail.

Dimensions (inches): 17.7 (w) x 8.7 (h) x 6.1 (d)

Link to soundclip ZABS blues PP 6G6. Made with a Fender strat ; amp plugged into 12’’ ence Fender speaker open cab; recorded with a mic; no eq or correction etc.

Roommate Mini Combo 5902

2007-04-19T14:05:00.000-07:00

The Roommate is a small single ended practise amp. When using the internal speaker you can easily use it at midnight without any trouble. This is a cheap PA speaker, rated 75 W , frequency response until 5 kHz. With a more efficient guitar speaker plugged in, it is loud enough to really enjoy the tube sound. The Roommate consists of two subminiature tubes: a 6112 triode in cascode followed by a 5902 pentode. The amp is switchable between Clean and Crunch. In the Crunch mode the amp becomes a hybride because a 2N5457 FET is used as first stage. With the gain of the FET only being about 4 x, the cascode stage gets driven a little harder and of course the pentode can be driven harder.
Output @ maximum volume is 700 mWatt. No tone control. The Roommate only has a Volume knob.
I recently changed the cascode stage into 2 preamp gain stages. The second half of the 6112 can really be overdriven and the pentode powertube can also be overdriven quite hard. I added just a little bitof feedback to keep the sound tight without loosing 'tube rawness'. Result: with the volume at half this amp sounds already like AC/DC .. Listen to the clip.
This set up gives the amp more character than the cascode to power tube set up.

For the power supply I used a torodial transformer with 3 secondary windings (9V-15V-15V); put those in series and multiplied that to 110V for the 5902 pentode and to around 220V for the 6112 triode cascode stage. The B+ for the FET is taken from the pentode rail and brought down with a RC to around 20V.
The 6.3V for the heaters is taken from the 9V secondary; I use a LM 317 and a transistor and a cap to avoid too much inrush current.
Dimensions (inches): 8.8 (w) x 8.8 (h) x 6.5 (d)

ZABS Vintage Rock 6G6

2006-12-11T12:40:00.000-08:00

The ZABS Vintage Rock 6G6 is a 'Zmall Amp Big Sounding' amp with several sound modes. Tube line out: first and second gain stage with 12AX7, followed by a push pull self split output stage with two tubes 6G6.

The amp is switchable between:

low voltage/low output triode: 200 mWatt
low voltage/middle output pentode: 1 Watt
high voltage/low output tiode: 500 mWatt
high voltage/more output pentode: 2.6 Watt

Each mode has a different sound; specially between triode and pentode the sound is different.
The amp is biased in Class A to Class AB 'hot'.
Also switchable is some extra drive for the output stage; especially when played in high voltage settings this drive adds some extra 'power' to the sound. It is a very suitable amp voor home practise.

The power supply unit uses a simple torodial transformer and voltage multiplier stages. The filament uses dc power supply.
Dimensions (inches): 10.4 (w) x 4.8 (d)

Link to 4 sound samples of every mode. Clips (about 60 secs each) are direct recorded; made with a Fender Strat; amp volume full open and with extra drive for the output stage. The song Heatwave is also made with this amp.

Firefly completed

2006-09-06T13:28:00.000-07:00

I already made a sort of prototype of the Firefly amp. But this is the completed version.

Dual Amp 6G6

2006-04-01T04:36:00.000-08:00

This is what finally has become of the PenOctal Amp. I've changed it into a dual amp with two channels. The clean one consists of a preamp penthode 6SJ7 and a switchable one knob tonestack. In that way there is a 'clean hi' position without the tone stack that provides some overdrive and a 'lo' position with the tone stack and less drive of the power tube. The drive channel has 2 preamp stages (ECC83/ECC81/7025) with a boost switch and gain pot; no tone stack. Power tube is the 6G6. Power supply unit is also switchable between solid state and tube EZ 80. Output about 1.5 Watt. It's a good sounding amp; the two channels give it a lot of possibilities. I use it at home as practise amp with a Jensen 10Q speaker.

PenOctal Amp 6G6

2005-10-28T14:43:00.000-07:00

This project started as the PenOctal Amp with EF86 - 6SL7 - 6G6 as power penthode. This is what you see at the picture. On the left is the EZ 80 rectifier tube. The amp uses a gain pot, one tone knob and master volume. Then I changed it into a sort of OctalFatness with a 6SJ7 - ECC83 - 6G6 and another 3-band tone stack. But again I've changed the whole amp. I just wasn't too happy with the sound.

Firefly Amp

2005-10-07T13:19:00.000-07:00

The Firefly is a push pull amp with a 'selfsplit' power amp. Output is around 1 Watt. There's no tone stack, but it does have a fine 'boost gain'.
Tubes and line up: 1 ECC 83 in cascade - 1/2 ECC 83 - 1/2 ECC 83 - power amp 1 ECC 81.
Output and power transformers are both of Hammond.
The amp sounds great and because of the 1 Watt you can stay friends with your neighbours.

Push-Pull Amp 6L6

2005-10-07T06:49:00.000-07:00

My first project; a push pull amp. The power amp uses 2 x 6L6 GC from Svetlana. Power 30 Watt. Tubes and line up: pre amp ECC 83 - tone stack - pre amp ECC 83 - phase inverter ECC 81 - power amp 2 x 6L6.
Tubes from JJ Electronics and Svetlana.
The amp uses toroidiol power and output transformers from Amplimo.

The sound is more or less like a Fender amp.

The loudspeaker box is also a DIY project with a 12 inch speaker Celestion Vintage 30.