Space Heater - simple tube preamp

[vigilante398]

I have rebuilt my Space Heater starting with a new board. After soldering and cleaning I examined the board for possible solder bridges and I once again hit upon this guy and sure enough get continuity across the solder joints. . . .
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I could swear that the two solder joints are not touching, but the meter says "yes". The schematic contained in the BOM is the old one and does not correspond to this layout, but from what I can deduce from the old schematic this could be the first stage plate resistor which is separate from the 220K further down the line by the 100n coupling cap which should prevent this "connection" from happening by design shouldn't it? And if this is the 220K contained in the PS then it DEFINITELY should not be happening. Nathan, can you please verify.

You're right and you're wrong. The 100k resistor is one of the plate resistors, and therefore one leg is connected to the HV rail. The 220k resistor is part of the feedback network of the power supply, one leg of which is also connected to the HV rail. Those two pads are supposed to be connected.

 

[Mike McLane]

So the points I'm describing are both on the "HV rail side" of the respective components with no other components in the path?

 

[vigilante398]

So the points I'm describing are both on the "HV rail side" of the respective components with no other components in the path?

Correct, it's okay if the solder wants to bridge those two pins because they're already connected in the PCB, and this is intentional.

 

[Mike McLane]

Now all I have to do is get those two 1M pots I FORGOT to order .

All dressed up and nowhere to go!!!

 

[kweefthief]

Everyone please ignore how one of the diodes goes in the wrong hole... What is the CLR thing on the top right supposed to be? The pcb looks a little different than the doc. Also is the white side for the top caps supposed to be positive?

 

[Nic]

White side would be negative I assume. Refer to the big 100uf
CLR would be led resistor ? ... 4k7?

Edit: the CLR is the Current Limiting Resistor for the led. I would believe that's what's peinted to let you use the best value depending on the type of led used and how bright you want it to be.

 

[vigilante398]

White side would be negative I assume. Refer to the big 100uf
CLR would be led resistor ? ... 4k7?

Edit: the CLR is the Current Limiting Resistor for the led. I would believe that's what's peinted to let you use the best value depending on the type of led used and how bright you want it to be.

Correct, white side of electrolytic capacitors is negative, and the CLR is indeed the current limiting resistor for the LED that's being mounted under the tube socket. Since this LED will be shining through a tube and won't be directly pointed at you I recommend using a lower resistance than usual to get it bright enough to be seen. I typically use 4k7 for CLRs, but on these I use 1k.

And I keep saying I'm going to update the doc with the new layout, and I continue to not do it :-/ I am not an organized person.

 

[kweefthief]

Im getting a squeal when i turn the gain up uh oh. Sorry about how dirty the soldering is! I noticed my IC wasn't in on both sides so i fixed that and tested again. Still squealing. Then, I tried another tube. Still squealing! Please help D:

 

[Dan0h]

Im getting a squeal when i turn the gain up uh oh. Sorry about how dirty the soldering is! I noticed my IC wasn't in on both sides so i fixed that and tested again. Still squealing. Then, I tried another tube. Still squealing! Please help D:
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Gotta put a buffer in front of these. Check other threads. Lots of chatting about it.

 

[kweefthief]

Gotta put a buffer in front of these. Check other threads. Lots of chatting about it.

Even when Im running it by itself? Thank you btw!

 

[Dan0h]

Even when Im running it by itself? Thank you btw!

Yup. The black eye and the space heater both have oscillation issues without a buffer in front for me. If you have any buffered bypass pedals put them in front of this and the squeal should vanish.

 

[kweefthief]

Yup. The black eye and the space heater both have oscillation issues without a buffer in front for me. If you have any buffered bypass pedals put them in front of this and the squeal should vanish.

hmm I got my keeley halo infront now and it's still squealing. Maybe it's an outlet problem? Pushing it with another pedal does the trick without squeal.

 

[kweefthief]

Im a low gain typa guy so I have a 12at7 in and it sounds so good. Running the super stevie in front of it ismagic. That combo turns my little blues jr into something else, even at lower volumes. Sounds more oomphy and bitey pushing it with the super stevie! Im not sure if it's my imagination but the space heater seems to fix the blues jr's bass issue a ton. Great stuff!

 

[Mike McLane]

To @kweefthief's experience. . . is the oscillation issue simply a "too much gain" issue given the circuit layout? I also find the SH has more gain on tap than I would typically need. If a 5751 or 12AY7 would tend to avoid the problem that would be great!

 

[Mike McLane]

I know the DIY Space Heater is going the way of the Dodo Bird, but just the same if I wanted to put a bass trim in it would putting a smaller sized coupling cap on a toggle be a good way to go?

 

[vigilante398]

I know the DIY Space Heater is going the way of the Dodo Bird, but just the same if I wanted to put a bass trim in it would putting a smaller sized coupling cap on a toggle be a good way to go?

Yup probably. You can experiment with smaller values to see how much bass you want to cut, 1uF is probably a good starting point but depending on what sound you're looking for you could go down to a couple hundred nanofarads.