unbalanced/balanced to balanced tube input

[Satyrnine]

I'm going to put together a mouser BOM for the ubaltobaltube shortly, unless someone has one they could share?

[Satyrnine]

The cap circled in green in the lower left has 100vdc across it. Having trouble finding a 6mm EL cap that size in ~120v+. Spend $25 on a tantalum? Just wedge an 8mm in there? Opa445's (I'm running 30v) are out everywhere in dip, so going smd+adapter. 

Can anyone give me a 101 on how to properly set the 1k (balance?) and 5k (bias?) trimmers?

 

Here's the link the to BOM for this board. https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=1d87f242f2

The circled cap in the BOM is an 8mm, and the socket is not available at mouser. 

Edited August 5, 2023 by Satyrnine

[spritzer]

8mm should fit in there just fine

[Satyrnine]

Grhv100 nearly ready to test, waiting on 90/8 trafo from toroidy and some shoulder washers for the to-220’s. Sink is temporary.

Added discrete bridge for heaters per Dukei/miroslav, who’s built a few.

Are the +- pads out from the smd relay for an LED? Warmup delay?

 

Any details on bias/balance adjustment on the tube board? Looks like plate balance and cathode resistor trim? 

 

Edited August 12, 2023 by Satyrnine

[penmarker]

On a scale of 1-10, how ok is it to use mica insulators instead of ceramic for the HV section?

[Pars]

On 8/11/2023 at 6:14 PM, Satyrnine said:

Are the +- pads out from the smd relay for an LED? Warmup delay?

I would guess that those are for turning on the opto coupler ( CPC1117NTR), same as the normal GRHV's have, for delay purposes. Haven't looked at the schematic for the 100, but for the normal GRHV, you have to apply a voltage to turn it on. You can leave the CPC1117 out if you don't need this feature.

I probably wouldn't use mica insulators for something like this (aluminum oxide instead), but I know mica has been used throughout the years for HV applications.

[justin]

1 hour ago, penmarker said:

On a scale of 1-10, how ok is it to use mica insulators instead of ceramic for the HV section?

What HV section?

[Satyrnine]

1 hour ago, penmarker said:

On a scale of 1-10, how ok is it to use mica insulators instead of ceramic for the HV section?

Oh hey, something I can answer! I'd give it a 6-7. My electronics experience is mainly with HV tube gear. I'm a repair tech and do custom builds, so lots of experience there. While Alum Oxide definitely IS better, we're only talking about 100v here, I don't think mica will give you any trouble. Be smart with thermal paste, as some types CAN be conductive and can cause a "bridge" if you're too generous with it. I've seen far worse than mica insulating 500+V successfully, but you should be OK. It's typically 600V insulation per mil of thickness. 

[justin]

another thing that gets people is not deburring their tapped holes

ive had to deburr entire batches of Aavid heatsinks before

 

Edited August 16, 2023 by justin

[Satyrnine]

1 hour ago, justin said:

another thing that gets people is not deburring their tapped holes

ive had to deburr entire batches of Aavid heatsinks before

 

Very good point, agreed! 

Always check for (lack of) continuity from device to sink before powering on as well,  obviously. 

[penmarker]

Ha, the mica insulation for the 100V section made me nervous. Its great that I shouldn't worry about it.

[spritzer]

12 hours ago, Satyrnine said:

Very good point, agreed! 

Always check for (lack of) continuity from device to sink before powering on as well,  obviously. 

I would also check for HV breakdown as there is continuity and then there is continuity at high voltages. 

[Satyrnine]

90vac transformers under 1M /s VA seem to be unobtanium. Think I can get away with 80vac and some low dropout diodes for the grhv100? Next available option is 100vac. Otherwise it's ~$250+ custom and 2-3 months wait min. Any off-the-shelf options I'm missing? Bonus points for 8vac + 90vac in one!

[Pars]

I would check with Toroidy in Poland. I had a pair of 6 secondary 100VA transformers done and they were pretty reasonable. Dual primary, 4x24V and 2x8V for either 57 EUR for their standard audio grade or 107 EUR for the audio supreme grade (I went with the audio supreme). They could do your 90Vac and 8Vac with no problems. Shipping was a bit high as is to be expected, but they came in about the same delivered as SumR, who I wouldn't use now.

[Satyrnine]

9 hours ago, Pars said:

I would check with Toroidy in Poland. I had a pair of 6 secondary 100VA transformers done and they were pretty reasonable. Dual primary, 4x24V and 2x8V for either 57 EUR for their standard audio grade or 107 EUR for the audio supreme grade (I went with the audio supreme). They could do your 90Vac and 8Vac with no problems. Shipping was a bit high as is to be expected, but they came in about the same delivered as SumR, who I wouldn't use now.

Thanks Pars, yeah that's what I meant with "custom". Audio Supreme was just under $250 (incl shipping) and 2ish month wait minimum. In 2x45vac (for 90vac) + 8vac. I'm not opposed to the cost if it's the only option, but off the shelf hammond toroids (if they actually made them in 90v and 8v) would be a fraction of that. Even if I had cheap temporary lam core iron to test with while waiting on toroidy would be great. Strange there's so few options in those two voltages. I'll just be patient I guess. Ughh. Haha!

[MLA]

Another option is https://www.mueller-rondo.com/eng/ in Germany.

They build exactly to spec, sometimes cheaper than Toroidy, and turnaround has been about a month on previous orders. 

[Pars]

The standard audio grade from Toroidy is the same transformer; just not encapsulated. It is screened, etc. just like the supreme, and at least for mine, was half the cost. Mine only took about 4 weeks from order to delivery.

I might consider the 100Vac transformer. You might need to deal with some extra heat, and ensure that component ratings are sufficient for that.

[justin]

If those are the only 2 options id go with the 100v

but if its a 115v primary not a 120 or you have high line voltage you’ll want to go to 200v+ rated caps

for this board the difference in heatsinking isnt going to be a lot

Edited August 22, 2023 by justin

[justin]

On 8/16/2023 at 1:15 PM, Satyrnine said:

Oh hey, something I can answer! I'd give it a 6-7. My electronics experience is mainly with HV tube gear. I'm a repair tech and do custom builds, so lots of experience there. While Alum Oxide definitely IS better, we're only talking about 100v here, I don't think mica will give you any trouble. Be smart with thermal paste, as some types CAN be conductive and can cause a "bridge" if you're too generous with it. I've seen far worse than mica insulating 500+V successfully, but you should be OK. It's typically 600V insulation per mil of thickness. 

I just realized, while working on a hand-drilled prototype, how much more likely it is for this type of thing to be problematic for a one-off or a DIY project that doesn't have CNC machined holes, pre-calculated lead bends, and things that result in the transistor lining up perfectly with the hole. Even many hand drilled/DIY projects where the transistor 'lines up' there may be force required to get it in place, a screw head going in at an angle - due to placement of the transistor, the hole drilled at an angle or both...all recipes for issues with insulators

Edited August 24, 2023 by justin

[Satyrnine]

7 minutes ago, justin said:

I just realized, while working on a hand-drilled prototype, how much more likely it is for this type of thing to be problematic for a one-off or a DIY project that doesn't have CNC machined holes, pre-calculated lead bends, and things that result in the transistor lining up perfectly with the hole. Even many hand drilled/DIY projects where the transistor 'lines up' there may be force required to get it in place, a screw head going in at an angle - due to placement of the transistor, the hole drilled at an angle or both...all recipes for issues with insulators

Definitely! I'm able to make plans/drawings to get all my holes drilled/tapped if I wanted to, but since I'm not planning on making multiples, I decided to just do all of that by hand, and have just the main front/rear panel cutouts done by Modushop. All the heatsink interface will be done by me by hand. I figure there are too many variables to be 100% sure with my placement until I have the chassis on-hand. What I do is drill the mounting holes first, then place the transistor without any thermal pad/compound, bend leads as needed, THEN apply thermal pad/paste, insert, solder. Def way more time consuming that having pre-drilled, pre-bent. I'm using shoulder washers for anything with a exposed tab/hole, to verify no continuity. I've found that forming taps tend to be less troublesome with aluminum than fluted cutting taps as well. 

[Pars]

Interesting. Where is a good source for forming taps?

[justin]

McMaster-Carr

[Satyrnine]

Trafo from Toroidy arrived! I'm getting about 7.2vdc for filaments, loaded. I'm currently using the stock 121R(series)/510R(to neg) resistors on the adjustable regs. Can anyone help me with the math to dial that in closer to 6.3vdc? 200R/510R? I assume that'd be easier on the regs than 121R/450Rish would?

[MLA]

That's the LT1085 regulator, right? Formula for setting voltage is on page 11 or 12 in the data sheet if I remember correctly. 

[justin]

Here is a low noise 100v supply i worked on just need another pack of batteries