Supro 1690T build

[shooter]

a single switch - everything on

STBY is an over-rated 20th century thing 

[sluckey]

STBY is an over-rated 20th century thing 

You should look at the schematic. Even pdf64 would approve.   

[shooter]

 
that took a minute to find!!!!
I went to bed a 1AM!!


I'll concede defeat on that one 

[dbishopbliss]

I'm missing the joke. :-/


But speaking of the standby. Was I correct in how/why it works in the Supro?


That is, according to Valve Wizard the "least bad way" to implement a standby switch for tube rectifiers is to place it after the first reservoir capacitor but before the output transformer.


But the Supro has nothing of the sort. The standby switch has one pole connected to the grid of V4 and the other connected to the grid of V5. My assumption is that when the switch is closed the out of phase signals are combined canceling each other so the amplifier will make no (or little) sound. I assume that leaving it out means exactly that... don't connect those grids to each other.



I assume pdf64 must be anti-standby switches. Perhaps that's the punchline... the standby on the Supro really isn't a standby, it's more of a mute switch, so even he would approve.

[shooter]

You got  it, it's a mute so it works for "us" NO-STBY crowd 

[dbishopbliss]

Here's an idea I have just to be a little different... Any reason I should not use one of these push button switches with the LED for a combined power on/off and indicator?



https://www.parts-express.com/SPST-Latching-Stainless-Steel-Waterproof-Tamperproof-19mm-Push-Button-Switch-with-120V-Red-L-060-944
https://www.parts-express.com/SPDT-Latching-16mm-Stainless-Steel-Tamper-Waterproof-Raised-Push-Button-Switch-with-Blue-Rin-060-958


I used the blue one on my recent attenuator build and I really like the feel of it. Just a light touch to turn off/on but solid feeling. I was thinking I could connect the LED to the heaters with a bridge rectifier and a resistor. This way, when you turn on the amp, the ring would light up.


Thoughts?

[acheld]

I can't think of a reason not to use one of these switches, though I wish I knew more about how they actually work.  They seem to be rated appropriately for US mains voltages. 

The two examples are different, of course.  The red one's light is operated off of mains voltage, where the blue one's light is intended for low voltages and is a separate circuit.   I like the simplicity of the red one, with no need for bringing the heater current back to the light. 

[dbishopbliss]

The red one's light is operated off of mains voltage... I like the simplicity of the red one, with no need for bringing the heater current back to the light.

I'm thinking the same thing. I guess I can buy one and connect everything before modifying the chassis. That's another nice thing about the red one, it takes a 3/4" hole instead of 16mm so I can use a step-bit to enlarge the hole for the power switch.

[dbishopbliss]

NBD - New Board Day! Is that a thing?


I got the board. One thing I forgot to do (or maybe you cannot do) is include holes for mounting the board on standoffs. You can see the pencil marks where I will be drilling.

[dbishopbliss]

Here's how the board will fit in the chassis.

[dbishopbliss]

The chassis was drilled for an output transformer that has 4 bolts. I need to drill 2 additional holes to mount this transformer. It's supposed to be for a Tweed Super 5F4 which was a dual 6L6 powered amp around 20 to 30 watts. I believe the original 1690T output transformer was undersized so the breakup may be at higher volumes. But, both of the amps I currently use breakup very early (Vox AC15 and Silvertone 1482) so having some headroom might be nice.

[acheld]

With regard to drilling mounting holes for your board:

It is likely that you will want to dismount your board at some point after you have installed components.  Often, you can get to the screws outside of the chassis to do this, but sometimes you will want to dismount the board from its standoffs.   Make sure that your screws are accessible without removing soldered components.   One of your pencil marks is directly in line with a turret path . . .

Yes of course I've made this mistake before . . .

[dbishopbliss]

I'm going to use the push-button on-off switch so I had to enlarge one of the hole to 3/4". I also enlarged the 5th hole from the left to accommodate the foot switch or the tremolo.

[dbishopbliss]

I have the transformers mounted. You can only see one of the mounting bolts here, but they are pretty brass ones that I got from Valvestorm. It was cheaper for me to buy a JTM45 mounting kit than try to get individual screws, nuts, etc. When I moved 2 years ago I got rid of all that stuff.

[dbishopbliss]

I should have checked this beforehand... those fancy brass bolts for the octal tube sockets are bigger than the holes drilled in the chassis.

[dbishopbliss]

No worries, pulled out my step bit again and enlarged the holes. Now I have all the sockets installed.

[dbishopbliss]

This is an accident waiting to happen. Because I am not using a dual can capacitor there is a large hole in the chassis that someone can easily reach into. Anyone know where I can get a plug to cover this up?

[tubeswell]

This is an accident waiting to happen. Because I am not using a dual can capacitor there is a large hole in the chassis that someone can easily reach into. Anyone know where I can get a plug to cover this up?

Easiest thing to do would be to make a cover out of a little square of sheetmetal, or install a dual cap can and use it for the plate/screen node supply only

[dwinstonwood]

If you scroll down on this page you'll see "Hole Blocker Plates." But, I'm not sure if the mounting holes match your chassis.

https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=MiscHardware&ORDER_ID=194341330

[dbishopbliss]

If you scroll down on this page you'll see "Hole Blocker Plates." But, I'm not sure if the mounting holes match your chassis.

https://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=MiscHardware&ORDER_ID=194341330

That’s what I was looking for… I was looking on the sockets page. I can always drill new holes if they don’t line up.


I could also install a cap for looks. I was digging through my box of parts and found some old caps that I never threw out. :-)

[sluckey]

I don't think those will completely cover that big hole. I would send Doug a pm and ask him to measure them. He usually responds pretty quickly.

[dbishopbliss]

I decided to go the cheap way out and use a 50/50 cap I had to cover the hole for now. I just discovered there is a "makerspace" 2 miles from me. It has all sorts of equipment including a metal shop, cnc machining and laser cutter. I can make my own plug in the future.

[dbishopbliss]

Another hole that was the wrong size. I bought the fuse holder from Valvestorm while I was buying the other screws, nuts, spacers, etc. It requires a 5/8" hole while the chassis has a 9/16" hole. Which seems an odd size, but that is what my calipers said. One lesson learned... maybe its better to buy chassis hardware from the same place you buy the chassis.

[dbishopbliss]

Everyone's least favorite part... I took the long road running the filament wires along the corners of the chassis. Because there are no signals flowing on that end I probably could have run the wires straight down towards the back of the amp.


I used the Valve Wizard method of wiring the filaments where you run the wire across the top of the socket. He claims any other method can induce hum.

[sluckey]

That's an odd looking fuse holder. What keeps it from turning when you replace a fuse?

[dbishopbliss]

HT wires connected to the rectifier. I had some N4007 diodes sitting in my drawer so I decided to follow Rob Robinette's recommendation and install diodes from terminals 3 to 4 and 5 to 6 just in case the tube fails. I thought I had some UF4007 diodes, but I expect these will work just fine.

That's an odd looking fuse holder. What keeps it from turning when you replace a fuse?

There are metal "ears" on the side that seem to expand when you insert the fuse holder into the chassis. It is VERY tight.

[dbishopbliss]

I installed the pots and jacks on the front panel to make sure they fit. Actually, I installed them on the back but then realized something... if I wire up the mains and fuse holder now then I will not be able to mount a rear plate without unsoldering them. Also, one of the speaker jacks is above one of the output tubes so it will be difficult to solder components to the socket if I install it now.


I need to start designing my face plates.

[dbishopbliss]

Ground bus and jumpers wired up using Hoffman's lacing style. There will be components sitting on top of those jumpers so I'm thinking that I might move those to the back of the board.

[dbishopbliss]

Speaking of the back of the board... I cut the insulation back far enough so the leads can go all the way through the turret and then wrap it over the top so it doesn't fall out.

By the way, Sluckey recommend the Kester No Clean flux to someone a while back. This is my first time using it... nice stuff. I love that it doesn't get all sticky like my old flux.

[dbishopbliss]

I started to dry fit components on the board and I realized a couple of things... First, I am going to have a very hard time installing the nuts to secure the turret board to the chassis. Second, some of the components are very close together which is going to make soldering cables very challenging.


I decided to same myself the aggravation and rework the board without the first two filter caps. I'm going to use a dual filter cap mounted to the chassis (fixed my hole problem) and spread out the rest of the components more. In addition, I'm leaving extra space on the ends of the boards for the standoffs. Because the rest of the components are spread out more, there is plenty of room for the center standoffs as well.


I guess this is what you learn from experience.

[dbishopbliss]

While I'm waiting for my new turret board to arrive I was doing a little thinking (which is dangerous).


According to the schematic, the primary of the original amp's OT was between 9K and 10K. The secondary was 1.6R (two 10" 3.2 ohm speakers in parallel). For easy math, let's say the primary was 9600 / 1.6 for a ratio of 6000:1.


Reportedly, Jimmy Page's amp was damaged and the speakers were replaced with a single 12" 4 ohm speaker. If I understand how things work, this means that the amp would now see a 24K load. According to the universal load line calculator, this makes for a very flat load line and like 11 watts power. If I recall correctly, I read that the amp was around 10 watts and runs cold so I think that makes sense.


My output transformer is 6000 / 4 for a ratio of 1500:1. If I plug a 16 ohm speaker into the 4 ohm secondary then the amp will see a load of 24K just like Jimmy Page's amp.


Do I have that right?

[dbishopbliss]

I got the new board in (black one). You can see that things are spread out more compared to the original board.

[dbishopbliss]

Another shot of the new board in the chassis. Lots more room for standoffs in the corner as well as in the middle. Looks a little steam punk with the steel and brass.


The old holes in the chassis will be for... ventilation. Yeah, that's it. Those holes are to keep things cool.

[Blues]

Reportedly, Jimmy Page's amp was damaged and the speakers were replaced with a single 12" 4 ohm speaker.

[...]

Do I have that right?

Well the 2x 10" speakers were replaced with a single Rola 12" 8 ohm speaker, not a 4 ohm one - you can verify directly by finding a back photo of the Sundragon Amp, it mounts a very nice 8 ohm Jensen P12Q.

I guess you have to re-elaborate your load consequently 

[dbishopbliss]

Well the 2x 10" speakers were replaced with a single Rola 12" 8 ohm speaker, not a 4 ohm one - you can verify directly by finding a back photo of the Sundragon Amp, it mounts a very nice 8 ohm Jensen P12Q.

I guess you have to re-elaborate your load consequently 

Well... I have two 16 ohm speakers I can run in series if I want to try it out.

[Blues]

Well... I have two 16 ohm speakers I can run in series if I want to try it out.

Worth a try, given that the 8 ohm load on 2 ohm OT is arguably the greatest "mod" on Page amp respect to the stock Coronado.
Incidentally, let me tell that IMHO the Sundragon demos I've watched aren't that attractive, the whole thing sounds grunted and lacking in bite to me - devil knows how Jimmy Page came up with that incredibile tone from it on Led Zeppelin I! 

[dbishopbliss]

Well... I have two 16 ohm speakers I can run in series if I want to try it out.

Worth a try, given that the 8 ohm load on 2 ohm OT is arguably the greatest "mod" on Page amp respect to the stock Coronado.
Incidentally, let me tell that IMHO the Sundragon demos I've watched aren't that attractive, the whole thing sounds grunted and lacking in bite to me - devil knows how Jimmy Page came up with that incredibile tone from it on Led Zeppelin I! 

Who knows... probably EQ and compression in the board. :-)


That said, I think the videos that Leon C has put out of his Coronado clones and original amps with the same circuit sound great (although I wish he did not record with his "wet rig"). I emailed him and he said he used the ClassicTone # 40-18060 which is the "Thunderbolt" transformer. The specs on that are no longer posted but I recently found out it has a 5K primary and rated for 35 watts so I'm in the ballpark with the Tweed Super OT.

[dbishopbliss]

I have the board almost fully loaded... somehow I'm missing one 0.047uF and one 0.0047uF capacitor on the right hand side. I also never submitted the order for the 6.8M resistor needed.


I used a different technique for installing the components this time. In the past I always put the leads into the holes of the turrets on the top. This time I wrapped the leads. I started on the left and got better as I moved right. I probably wrapped too much on those first components. That said, they have very strong mechanical connections. I could probably fire up the amp now without any solder and it would probably work (not going to try it).


In retrospect, I would not install the jumpers between turrets on the top of the board in advance. Things are getting a little crowded in places. Instead, I would wrap the lead around the turret and leave it long so it extends to the next turret.


I plan on installing all the leads to the sockets, pots, jacks, etc under the board. I will strip enough insulation back so the lead can go all the way through the turret and then bending over the top.

[dbishopbliss]

I have a couple of other caps I could use but it will be hard to make them fit so I'm going to wait for the new ones to arrive. Interesting to compare the size of these vintage caps to the size of the modern sozo cap on the lower left hand side.

[PRR]

.... I could probably fire up the amp now without any solder and it would probably work (not going to try it)....

Bogen did that once. ONE of the 100+ connections was crimped but the solderer missed it. It ran for years in heavy duty (driving a motor) until it caught fire and was thrown-out (I caught it).

[Sonny ReVerb]

Which rectifier did you decide on? The 5V4G datasheets I looked at only show a max 32uF first filter cap. Your 47uF might cause it to arc. The 5AR4 can handle up to 60uF, so you would be fine there.

[dbishopbliss]

Which rectifier did you decide on? The 5V4G datasheets I looked at only show a max 32uF first filter cap. Your 47uF might cause it to arc. The 5AR4 can handle up to 60uF, so you would be fine there.

I'm using a 32uF cap and I will probably be going with a 5AR4 because the voltage of my PT is lower than the original PT. I think things will work out because mains are higher and 5AR4 has lower voltage drop, but if the voltage is too high I figured I could swap in different rectifier tubes.


That said, I didn't realize filter caps had max values... The first several datasheets I looked at did not have a value listed at all. One of them says the *typical operation is 10uF.  Then I noticed footnotes that say things like,

when filter condensers larger than 40uF are used, it may be necessary to add additional plate supply impedance

when a filter-input condenser larger than 40uF is used, it may be necessary to use more plate-supply impedance than the minimum value show to limit the peak plate current to the rated value.

How do I increase the plate-supply impedance? I don't know what that means.

[sluckey]

How do I increase the plate-supply impedance? I don't know what that means.

I like to use two power resistors (50, 100, 200Ω, etc. @5 watts), placed between the PT HT wires and pins 4 and 6 of the rectifier socket. Resistors can be mounted directly on the socket using spare pins.

However, I don't think this will be necessary with a 32µF filter cap at node A.

[bmccowan]

I take everything about the JP amp with a grain of salt. For decades Jimmy claimed he could not remember the details of that amp. Then the opportunity to make money off a "historically accurate" clone of that amp jogged his memory. I'm not dissing this project as I love Valco amps. But the story of the Sundragon just does not add up for me. I agree with the comments about the studio EQ and such contributing to that tone. My favorite players are Ry Cooder and Richard Thompson - the only thing that will get me close to their sound/tone is practice. And at my advanced age; it ain't going to happen, but building amps is fun; so I continue.

[dwinstonwood]

My favorite players are Ry Cooder and Richard Thompson

"Red hair and black leather, my favorite color scheme"
I've seen Thompson a few times. It's mesmerizing to watch him play.

[dbishopbliss]

I take everything about the JP amp with a grain of salt. For decades Jimmy claimed he could not remember the details of that amp. Then the opportunity to make money off a "historically accurate" clone of that amp jogged his memory. I'm not dissing this project as I love Valco amps. But the story of the Sundragon just does not add up for me. I agree with the comments about the studio EQ and such contributing to that tone. My favorite players are Ry Cooder and Richard Thompson - the only thing that will get me close to their sound/tone is practice. And at my advanced age; it ain't going to happen, but building amps is fun; so I continue.

I'm actually not a huge Led Zeppelin fan. I knew the music because I grew up with it, but I was more into The Who. However, every time I listen to clips of Supro amps I really like their tone. Just so happens I liked Leon C's clips of the 1690T the best. Then I searched out others to confirm my preference of that model over other Supros so here we are.

[bmccowan]

Leon's clips are great! Every time I listen to his clips I want to build the amp he is playing. He is a master of his crafts - amp building and guitar playing. My favorites are the older all octal Valcos, but this amp is also right up there. I have an original upper and lower chassis along with a stripped cabinet of this amp awaiting attention. The two chassis have suffered many indignities which is why I keep passing over the project.

[bmccowan]

"Red hair and black leather, my favorite color scheme"
I've seen Thompson a few times. It's mesmerizing to watch him play

Yes it is. I have seen him more times (10+) than any other artist and will see him again in Boothbay Harbor, Maine in September. His playing is impeccable and he rapport with the audience is amazing. If any here are unaware - go to youtube and watch the various versions of 1952 Vincent Black Lighting which is the source of Dwinstonwood's quote. Acoustic and electric he is a master.

[drew]

I have the transformers mounted.

Do you know about the "headphone trick," and have you used it to verify that the way you have the transformers mounted will be the lowest noise way?  If not, you might want to look into this before you finalize your circuit board and start hooking everything up.

[dbishopbliss]

Do you know about the "headphone trick," and have you used it to verify that the way you have the transformers mounted will be the lowest noise way?  If not, you might want to look into this before you finalize your circuit board and start hooking everything up.

Nope... I don't know the trick. The chassis is pre-drilled for a JTM45 so I'm not sure how much flexibility I have mounting the transformers. The PT is a lay down transformer so it cannot move. I could drill additional holes for the OT and re-orient it 90 degrees (or some other angle) or move it further away from the PT because there is no choke like the JTM45 has.


This is what I found

First set up the power transformer. If it's not installed yet, all the better, but if it is, this will still help. If the PT is not installed, wire up the primaries to a power cord, but do not wire up any secondaries-- tape the ends of the secondaries. If the PT is installed, fine, just make sure there is no circuit on any of the secondary leads (pull all tubes, and disconnect leads and tape them as necessary).Now set up the signal transformer (output, reverb, whatever). Hook one set of OT secondaries (your choice, but I usually go from ground to the highest impedance tap, don't worry about impedance matching here!) to a set of headphones. Tape the primary leads.Put the headphones on, plug in the power cord, and start moving the signal transformer around. Try it all over the chassis, and also rotate it. While you might expect the least hum with the transformers as far from each other as possible and at right angles (and that may be the case for you), it might come at an odd angle and/or position. Sometimes the least hum occurs when the transformers are side by side. When you find the quietest spot, use a permanent marker to mark where the mounting holes should be.