Friday, July 17, 2009
Boost pedal 12AU7
Just a little summer project. It’s a simple two stage boost pedal using a 12AU7 at a B+ rail of 12 Volt. True bypass switch, a volume pot and on-off led; that’s it. The gain of this pedal is modest; giving just a nice volume boost. The tube also shapes the sound just a little, giving it a nice extra fat tube sound. I use this pedal in front of my ZABS Champ and it works great. The schematic can be found at: tubetown.de
Friday, January 16, 2009
Tremolo in a Fender Bassman
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)
Sunday, October 19, 2008
ZABS Champ XL
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. And I added the 6SJ7 pentode just like the Champ 5C1. So now the first preamp can be switched between 12AX7 and 6SJ7. That is a great sounding tube by the way! Almost like the amp has a little reverb.
Other possibilities:
NFB can be switched 'on', 'less' or 'off' for a tight or a more raw sound. And 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.
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. And I added the 6SJ7 pentode just like the Champ 5C1. So now the first preamp can be switched between 12AX7 and 6SJ7. That is a great sounding tube by the way! Almost like the amp has a little reverb.
Other possibilities:
NFB can be switched 'on', 'less' or 'off' for a tight or a more raw sound. And 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.
Monday, February 11, 2008
ZABS blues PP 6G6
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. 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.
The long tail phase inverter uses a 12AT7. The push pull poweramp uses 6G6 pentodes. 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.
Thursday, April 19, 2007
Roommate Mini Combo 5902
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.
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)
Output @ maximum volume is 700 mWatt. No tone control. The Roommate only has a Volume knob.
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)
Monday, December 11, 2006
ZABS Vintage Rock 6G6
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.
Wednesday, September 06, 2006
Firefly completed
I already made a sort of prototype of the Firefly amp. But this is the completed version.
