can i use a 811A in this guitar amp circuit?
https://www.tedweber.com/media/kits/lauren_schem.jpg
PT specs
680V/150ma
6.3V/5A
solid state rec used.
OT specs
25watt SE
5000k primary
2/4/8/16 secondaries
i wanted to build a guitar amp that was a bit unusual ish so i found this weber Lauren amp kit and loved the cool 807 tube it uses. i never messed with 807s before but after doing some closer spec checking on the transformers this kit comes with, i realized i could be runing a more powerful output tube.
then i heard about the 811A and got curious lol
but i want an opinion from people with more XP with these tubes. if an 811A is just a bad idea with these transformers & circuit design, what other tube could i use in place of the 807 in this schematic to really get some umph?
thanks!
https://www.tedweber.com/media/kits/lauren_schem.jpg
PT specs
680V/150ma
6.3V/5A
solid state rec used.
OT specs
25watt SE
5000k primary
2/4/8/16 secondaries
i wanted to build a guitar amp that was a bit unusual ish so i found this weber Lauren amp kit and loved the cool 807 tube it uses. i never messed with 807s before but after doing some closer spec checking on the transformers this kit comes with, i realized i could be runing a more powerful output tube.
then i heard about the 811A and got curious lol
but i want an opinion from people with more XP with these tubes. if an 811A is just a bad idea with these transformers & circuit design, what other tube could i use in place of the 807 in this schematic to really get some umph?
thanks!
Moved to Instruments and Amps
The 811A is a transmitting triode with a Mu of 160. It will not work in a cathode biased circuit on 400 volts or less, since with zero or any negative bias it will draw no current. You could rig up a way to bias the grid positive, but then it is a low impedance....too low to be driven from a 12AX7. The high Mu also can result in hum with AC on the filament since there is no cathode sleeve.
ok thank you for clearing that for me!
does anyone have a good idea of what tube i could use in place of the 807 for more output?
does anyone have a good idea of what tube i could use in place of the 807 for more output?
The 807 is a derivative of the 6L6GA. A 6L6GC could be pushed a bit harder, but for maximum power run a KT88 or 6550, and use a lower impedance OPT (around 3K ohm) a higher voltage power transformer or both.
Here is the schematic of amp I called the Turbo Champ. I built a few of these in the late 1990's. No two were the same, and this schematic was drawn up after the fact, and may not exactly match any specific amp.
Many were made with car stereo speakers obtained cheap when a local K-Mart closed down. A couple were made in traditional 6V6GT on 350 volts style, but most ran a Chinese KT88 or Sovtek 6550WA on 450 volts. They were LOUD!
Each had some unusual combination of switches and pots to make it different from the others.
Here is the schematic of amp I called the Turbo Champ. I built a few of these in the late 1990's. No two were the same, and this schematic was drawn up after the fact, and may not exactly match any specific amp.
Many were made with car stereo speakers obtained cheap when a local K-Mart closed down. A couple were made in traditional 6V6GT on 350 volts style, but most ran a Chinese KT88 or Sovtek 6550WA on 450 volts. They were LOUD!
Each had some unusual combination of switches and pots to make it different from the others.
Attachments
thanks tubelab!
i was just thinking about KT's like an 88 or a 90. and for giggles i was looking at a 150 xD
you mentioned 3K OTP would be better but what about runing an 8 ohm cab in the 16 ohm tap? i used this trick in the past to get better primary impedances for the tubes i was using.
anyway with a 5k Primary, this trick would bring it down to 2.5k which is closer to 3k then 5k
thoughts?
thanks!
i was just thinking about KT's like an 88 or a 90. and for giggles i was looking at a 150 xD
you mentioned 3K OTP would be better but what about runing an 8 ohm cab in the 16 ohm tap? i used this trick in the past to get better primary impedances for the tubes i was using.
anyway with a 5k Primary, this trick would bring it down to 2.5k which is closer to 3k then 5k
thoughts?
thanks!
That works. I have a 20 watt SE HiFi amp on my bench right now. It is using a big 5K Hammond with the 8 ohm load on the 16 ohm tap.
The OPT in most of the Turbo Champs was a multi tapped Hammond 125CSE. There was a switch to select every tap, as each had a different sound. Be wary of going too far the other way, running 8 ohm or higher speakers on a 4 ohm or less tap. The light loading on the tube can allow too much voltage to build up in the OPT when the amp is driven hard into clipping. Sparks inside the OPT can ruin your day.
An "8 ohm" guitar speaker can be 30 ohms or more when driven hard at its resonant which usually falls in the guitar's frequency range.
Remember also that the bigger tubes require a bigger power transformer to feed them, both for the heater winding and the B+. Single ended amps are rather inefficient. To get 20 watts out of one, you will need 50+ watts of B+, maybe 450 - 500 volts at 100mA or more.
The OPT in most of the Turbo Champs was a multi tapped Hammond 125CSE. There was a switch to select every tap, as each had a different sound. Be wary of going too far the other way, running 8 ohm or higher speakers on a 4 ohm or less tap. The light loading on the tube can allow too much voltage to build up in the OPT when the amp is driven hard into clipping. Sparks inside the OPT can ruin your day.
An "8 ohm" guitar speaker can be 30 ohms or more when driven hard at its resonant which usually falls in the guitar's frequency range.
Remember also that the bigger tubes require a bigger power transformer to feed them, both for the heater winding and the B+. Single ended amps are rather inefficient. To get 20 watts out of one, you will need 50+ watts of B+, maybe 450 - 500 volts at 100mA or more.
ok thanks for the help! the PT has 150ma on the high voltage and 5A on the heater winding so it should be fine with bigger tubes, im also gonna run this amp with a 6SL7 in place of the 12AX7 cuz BIG PREAMP TUBES! 🙂
Want to show off big preamp tubes. Find a pair of glass 6SF5GT's. They are nearly identical to half of a 12AX7. 6SQ7GT's are almost the same too, just leave the diode plates unconnected or grounded.
Both of these were also made in metal envelopes, same number, no GT (glass tube) on the end.
I plan to make a guitar amp with them and a pair of metal 6L6's or 6V6's, not sure which yet......MetallicAmp, all tube, no glass!
ok thanks for the tip! i will use a 6sl7 for this one cuz i already have it but im sure i'll be making more amps with bigger preamp tubes in the future so i will keep them in mind =)