Valve Art KT66 vs????

[Dave H]

why don't the many JTM45 layouts use pin1 to park one side of the grid stop, like the Fenders do.

...he used these pins that look like they screw into the chassis, but there's an insulator then a pin on top, so you can solder stuff to the top and it won't ground to the chassis (I think anyway).

I think the JTM45 layouts have pin 1 connected to pin 8 so that EL34s can be used. Pin 1 is g3 on EL34s.

The 'pins' with the 1 ohm bias check resistors look like sockets for the rear panel bias test points.

[dstrat]

Try here:

https://www.mouser.com/Test-Measurem...+plugs&FS=True

[mikepukmel]

Cool, thanks. Dave, didn't know EL34's were that close. Dstrat, thanks for the part link.

[soundmasterg]

Feel kinda stupid now, I think its a banana plug jack? Mount 3, put two bias check resstors between, then the middle would be grounded,. I think.

The best ones to use for bias test points are not banana jacks. They are tip pin jacks. They come in red and black, so you can get a black for ground, put it in the middle, and put two reds one on either side, and run the 1 ohm resistors between those and the black one. See the link below.

Greg

https://www.tubesandmore.com/product...sulated-deluxe

[mikepukmel]

Cool thanks Greg! This idea is awesome. And if I mount the pin jacks in the right spot, the cathode ground wiring won't be all that crazy. Would be very nice to not have to open the amp up to check the current. I think I'll try something like that on both builds, although there's not a heck of a lot of extra room on the back of fender style chassis. Thanks for the link!

[soundmasterg]

Cool thanks Greg! This idea is awesome. And if I mount the pin jacks in the right spot, the cathode ground wiring won't be all that crazy. Would be very nice to not have to open the amp up to check the current. I think I'll try something like that on both builds, although there's not a heck of a lot of extra room on the back of fender style chassis. Thanks for the link!

Sure no problem. One thing I've done in the past is to put two red tip pin jacks with a black in the middle, and the 1 ohm resistors going from red to black for each tube, and then black to my ground point, but I have also added one with a voltage divider to the B+ so I can get the B+ divided by 50 if its 500V. You want to make sure you divide it down so there is no shock hazard on the outside of the chassis. This way you can check the B+ and the bias without opening the chassis. If you have a cathode bias amp, you would want the cathode voltage on the back of the chassis also to get an accurate result. See the pic for what I did on a Bogen CHB100 that I gutted and built.

The tip pin jacks allow you to just plug your meter lead in and get a reading.

Greg

[mikepukmel]

Sure no problem. One thing I've done in the past is to put two red tip pin jacks with a black in the middle, and the 1 ohm resistors going from red to black for each tube, and then black to my ground point, but I have also added one with a voltage divider to the B+ so I can get the B+ divided by 50 if its 500V. You want to make sure you divide it down so there is no shock hazard on the outside of the chassis. This way you can check the B+ and the bias without opening the chassis. If you have a cathode bias amp, you would want the cathode voltage on the back of the chassis also to get an accurate result. See the pic for what I did on a Bogen CHB100 that I gutted and built.

The tip pin jacks allow you to just plug your meter lead in and get a reading.

Greg

How cool is that, thanks, what a great idea. I was very worried about futzing with any of the HV wiring. If you let the amp break in a bit, then measure the HV, does it change much? I will definitely put the current measuring pins in not sure I have enough room on the thin fender chassis for the divided HV. But ... the Marshall style chassis has loads of room back there!!

[bob p]

if you've got a cramped back panel, you can also mount pins on the top of the chassis, assuming that your leads will be short enough to fit into the jacks without removing the chassis from the cabinet.

if you do decide to do the HiV pin jacks, keeping them off of the back panel and out of sight wouldn't be a bad idea... especially if you have kids that like to poke pointy things into holes. for an HV port I'd prefer something with a cap or a cover. i wonder if anyone makes pin jacks with spring-loaded covers.

[soundmasterg]

When I do the HV tip pin jack, it is divided down, so if the amp has B+ of 483V then my tip pin jack is at 4.83V so there is no safety hazard. I tried 48.3V but it was perfectly accurate when divided down further so I went with the safer option. I would guess that if I was making a commercial amp, then they would require the reduced B+ to be on the top of the chassis under a cover, clearly marked with warnings, etc., so someone wouldn't try to stick something in the tip pin jack. For the one amp I built for commercial sale I did put that jack on top of the chassis in a place that wasn't easily accessible from the outside of the amp unless you were looking underneath (upside down chassis like a blackface Fender), and it was clearly marked with warnings near it with an arrow pointing to it, though I didn't use a cover.

The B+ doesn't change any differently as the amp warms up when using the tip pin jack or not, but that said, it will change a bit as it warms up but the bias voltage is changing too as it warms up and the tubes settle in. It is easy enough to check it after you have played it for 10 minutes and see for yourself. Of course if you adjust the bias, the voltage will change too, so it is a good idea to check the B+ when you adjust the bias voltage and then recalculate the proper bias.

Greg

[kHz Tube Amps]

The prices on VA seem to have taken a jump since the last time I looked. I'd have to say, not much point in trying KT66 unless you're really willing to spring for the extra cost, just for an experiment. Also, the glass bulbs are a bit larger than 6L6's and you may have a tough time wedging them into a Bassman head box. On combo amps the extra weight helps gravity drop them from their sockets.

Haven't personally seen any "Gold Lion" genelex so-called reissue KT66. But I recently had a look at their KT88. Inside the glass, looks exactly like Sovtek/EH KT88 and 6550. I wouldn't be surprised if it's yet another of New Sensor's tricks, applying a venerable logo to the glass and charging an premium price while claiming the product is an "authentic reproduction." Might be much the same for Valve Art - I see a 6L6 plate in a big bulb, big deal. But there's no way know for sure without buy, try, and maybe dissect one and compare it to the original item.

In fact I DO keep a pair of real original Genelex KT88 boxes on the shelf for nostalgia's sake. How did you know ???

I don't know anything about base wired to pin 1 on any of these. And it's not grounded unless you ground it. These are beam tetrodes so pin 1 presumably isn't attached to any of the tube elements anyway. You would only have to worry if it was jumpered to pin 8 on the socket, as it often is, and you're running a self-bias circuit.

I have a pair of Shuguang KT66s & a pair of the Genalex gold Lion KT66s. I've tried both in a 1483 Silvertone head, THD Bivalve and a Rivera era Fender Concert combo. I find both to sound very big /w/ lots of bottom and tasty mids. I didn't hear a substantial difference between them though. I say save your money and do the Sino thang.

[mikepukmel]

if you've got a cramped back panel, you can also mount pins on the top of the chassis, assuming that your leads will be short enough to fit into the jacks without removing the chassis from the cabinet.

if you do decide to do the HiV pin jacks, keeping them off of the back panel and out of sight wouldn't be a bad idea... especially if you have kids that like to poke pointy things into holes. for an HV port I'd prefer something with a cap or a cover. i wonder if anyone makes pin jacks with spring-loaded covers.

Thanks Bob. There's this video by Mr Carlson's lab. He's working on an ancient tube amp. Can't remember what it was exactly, someting from the 40's maybe. Anyway, I think the speakers had electromagnets, and there were these high voltage connections right on the back of the amp, screws that you wire down to the speakers to power the electromagnet. It was scary high voltage too, not like 20 or 30v that would give you a jolt. Can't recall exactly, 300v maybe? Heh. back in the day.

[mikepukmel]

When I do the HV tip pin jack, it is divided down, so if the amp has B+ of 483V then my tip pin jack is at 4.83V so there is no safety hazard. I tried 48.3V but it was perfectly accurate when divided down further so I went with the safer option. I would guess that if I was making a commercial amp, then they would require the reduced B+ to be on the top of the chassis under a cover, clearly marked with warnings, etc., so someone wouldn't try to stick something in the tip pin jack. For the one amp I built for commercial sale I did put that jack on top of the chassis in a place that wasn't easily accessible from the outside of the amp unless you were looking underneath (upside down chassis like a blackface Fender), and it was clearly marked with warnings near it with an arrow pointing to it, though I didn't use a cover.

The B+ doesn't change any differently as the amp warms up when using the tip pin jack or not, but that said, it will change a bit as it warms up but the bias voltage is changing too as it warms up and the tubes settle in. It is easy enough to check it after you have played it for 10 minutes and see for yourself. Of course if you adjust the bias, the voltage will change too, so it is a good idea to check the B+ when you adjust the bias voltage and then recalculate the proper bias.

Greg

Thanks Greg, will do. The last few times I was a bit scared, but learning where not to put my hands when the chassis is running and open. The pin jacks arrived, fiddling for a good spot to mount them in both amps.

[Justin Thomas]

I've only jolted myself once while working on a live amp; what I've done more of is doing some level of disassembly, walking away for a day or two, then finding out my memory is not as good as I like to think... I've put some resistor connections back in the wrong place, and flamed a few out. That's when I learned the SECOND Cardinal Rule of Amp Repair:

TAKE PICTURES. GOOD ONES. Right after "Probe with ONE hand, and keep the other in your pocket. Well, learning where NOT to poke around!

Justin

[mikepukmel]

I've only jolted myself once while working on a live amp; what I've done more of is doing some level of disassembly, walking away for a day or two, then finding out my memory is not as good as I like to think... I've put some resistor connections back in the wrong place, and flamed a few out. That's when I learned the SECOND Cardinal Rule of Amp Repair:

TAKE PICTURES. GOOD ONES. Right after "Probe with ONE hand, and keep the other in your pocket. Well, learning where NOT to poke around!

Justin

Heh, thanks Justin. I got zapped once, luckily after the amp had bled down some. I didn't put my fingers inside the amp, but was pulling the chassis out, and got my hand too close to the standby switch, which in this clone, the pins on the standby switch stick up pretty far. Too far. Definitely going to unsolder the wiring, put some heat shrink, re solder and shrink around those connections.

[soundmasterg]

When I was first messing around with tube amps in the early 90's I shocked myself with 525V DC, but luckily no tubes were in the chassis. I was doing a stupid rookie mistake...checking voltages with both hands while resting one arm on the upside metal chassis!!! One minute I was measuring with my meter and the next I was 6 feet across the room jammed against a dresser, and feeling like someone had beat me up! Decided then and there to take a step back and learn a bit before I kill myself! Haven't regretted it at all, and that interest in learning about it ended up leading me to engineering school, where they haven't taught tubes in 50 years, but I still learned a lot. I'm very careful since back then and I haven't shocked myself since then either. It pays to be safe with this stuff for sure!

greg