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An old Vac tube from a guitar amp. Shot for Macro Mondays 2" o r less theme. This item is exactly 2" tall and about .75" diameter. I've had this kicking around for a good 20 years. No longer play guitar, but it was too cool to throw away.
It is sitting on an old piece of circuit board from some sort of scientific test equipment I dismantled. I think this was from the mid 80's. It is a cool translucent green. LED light below reflecting on the glass. Background is lit from, the below LED light. It is a circuit board from a more modern computer. I have a stash of boards, and hard drives taken apart just for photos.
Title inspired by the 80's movie "War Games". I watched this tonight after a contact of mine mentioned it in a comment to another photo I posted.
Full gallery of images here: olydemon.com/essays/2013/11/macro-mondays-2-inches-or-less/
This 5881 tube was removed from an Engl guitar combo many years ago. Probably a Russian Sovtek manufactured item.
Home made valve power amp based on the old Mullard 5-20 with some fairly significant tweaks.
Valves:
GE 6267
GE JAN 6CG7/6FQ7
Electro Harmonix 6CA7EH
Sovtek 5AR4
Iron:
Sowter UA21 outputs
Primary Windings mains
VVT chokes
Current schematic:
Light is a partial mix of sunset through my window, reflection of my monitor and a torch shone through my fingers. (giving a red light) It's ended up producing some rather psychedelic colours.
Amp is a take on a Mullard 5-20 using a 6CG7 as the phase splitter with a CCS in it's tail. It uses a GE 6267, Electro-Harmonix 6CG7, EL34/6CA7/KT77 and a Sovtek 5AR4. Output transformers are Sowter UP21S. (6K6 / 43% UL taps with a 4/8/16R tapped secondary.)
Schematic for those that are interested.
www.flickr.com/gp/39959182@N05/083n1w
Taken using a Nikkor 28mm f2 AI-s
A more compact version under test along side the larger MK III prototype. Cobbled together with bits of previously used wood and an old 19" 6U aluminium rack blanking cover.
Basic specifications are:
6059/CV4006 input pentode running as pentode
6CG7/6FQ7 phase splitter as LTP with a constant current sink in the tail
6CA7/EL34/KT77 push pull output at ~450V with cathode bias (around 19-20W idle dissipation using zeners to tighten things up towards fixed bias)
Sowter UP-21 output transformers, VVT chokes & Primary Windings HT transformers.
Valves:
Mullard EF86
GE JAN 6CG7
Electro Harmonix 6CA7EH
Sovtek 5AR4
Iron:
Sowter UA21 outputs
Primary Windings mains
VVT chokes
I've made some changes to the design as the gain was too high and I couldn't resort to simply increasing the feedback in order to reduce it. The change allowed for a reduction in open loop gain and also a small increase in feedback level too. This successfully dropped the gain from 49.54dB open loop and 33.26dB closed loop to 45.77dB open loop & 25.87dB closed loop. That also took feedback from 16.5dB to 19.9dB.
Current schematic:
After refurbishing the RCA console amp, the new Sovtek tubes could not handle the voltage and had to reduce the incoming voltage to get them to stop. The original RCA tubes had no issue with the higher voltage. This was my first tube amp. You can see the final product in my other photos.
My NOS input tubes finally arrived, and after only a few hours break-in, I have to say that they sound phenomenal. Huge improvement over the stock Sovteks that the Oto SE shipped with. These are the valves that Peter Qvortrup of AN UK personally recommended to Steve Hoffman for this amplifier... so after waiting six weeks to get a closely-matched pair (same date codes and factory, and testing within 2% of each other) I have to agree with Peter.
Our Fender Twin (1965 RI bought in 2000) was rewired point-to-point by George Alessandro. New Sovtek power tubes, new Alessandro (USA Eminence) speakers. Both channels get reverb & tremolo. Left channel voiced darker like a bassman.
Amp is a take on a Mullard 5-20 using a 6CG7 as the phase splitter with a CCS in it's tail. It uses a NOS GE 6267, Electro-Harmonix 6CG7 & 6CA7 and a Sovtek 5AR4. Output transformers are Sowter UP21S. (tapped version of the UA21)
Power tansformers are primary windings for a mullard 5-20 and the chokes are made by VVT.
I've now tried Tung-Sol EL34B, JJ KT77 and these 6CA7. They all sound good but I have to admit to really liking these 6CA7's a lot.
Mullard EF86
GE JAN 6CG7
JJ KT77
Sovtek 5AR4
Sowter UA21 output transformers, Primary Windings mains transformers and VVT chokes. Schematic:
www.flickr.com/gp/39959182@N05/FgD291
I also have GE 6267's, EH 6CG7, EH 6CA7 and Tung-Sol EL34B's which all work very well too. I'm sticking with the matched pair of KT77's as the other valves are matched quad's for when both amps are built.
Prototype in testing. Has been working great for the last month. Working on trying to shrink it down slightly in order to more easily fit two monoblocks on a shelf in proper aluminium chassis.
Mark IV prototype which has been under test for about 2 months.
Specifications are:
Brimar 6059/CV4006 input pentode running as pentode (Industrial version of a 6BR7)
GE 6CG7/6FQ7 phase splitter as LTP with a 2SC2611 used as a constant current sink in the tail
Tung-Sol EL34 push pull output at ~450V with cathode bias (around 19-20W idle dissipation using zeners to tighten things up towards fixed bias)
Sowter UP-21 output transformers, VVT chokes & Primary Windings HT transformers.
My NOS input tubes finally arrived, and after only a few hours break-in, I have to say that they sound phenomenal. Huge improvement over the stock Sovteks that the Oto SE shipped with. These are the valves that Peter Qvortrup of AN UK personally recommended to Steve Hoffman for this amplifier... so after waiting six weeks to get a closely-matched pair (same date codes and factory, and testing within 2% of each other) I have to agree with Peter.