DIY Valve Guitar Amp Head

While looking through Evatco's range of capacitors, I saw that they had every value of Cap I needed in 500V silver micas except 470pF, but, they did stock a 500pF/500V silver mica, which I'm going to use as a substitute for 470pF, there's only a difference of 30pF in value which I think is not worth worrying about, I was hoping to buy all the other cap values I needed in 630V yellow tubular RT style caps but they don't seem to stock any .022uF/630V ones, they do however stock .022uF/500V Blue Molded Sozo brand caps in stock that look like these:

https://www.evatco.com.au/sozo-500v-capacitors

They are a little pricey but I'm not worried, they seem to be very good quality caps, actually I've heard lots of good things about Sozo caps, never tried them before so this scratch-build amp project is a good excuse to do so.

Evatco don't seem to stock any 200uF/350V multi cap cans, but I did find another online company that sells 200uF/500V multi cap cans, I need two for this scratch-build project, so I'll order a couple of them.

Update:

Today, I'm in the process of making a couple more Tagboards for my diy scratch-build Soldano SLO-50 guitar amp, one of the tagboards is for generating the -V Bias supply for the two KT-77 power tubes, they will not operate correctly in the amp without it, the other tagboard is for generating the +V High Voltage supplies for all the preamp and power tubes, again, the amp will not operate correctly without it.

Update:

Just a quick update so you can see where I'm at in the build progress, I finished making all the tagboards I needed to make in order to mount all the components needed to make the amplifier work, here's a pic showing all the tagboards mounted in the amp chassis, all that's left to do is to finish populating them with parts, mounting the new transformers and etc that I need to order, and then do all the final wiring-up before doing the initial bias adjustment and tests to see if everything is operating correctly, and then comes the fun part, testing it out with my Ashton Quad Box and a guitar.

Attachment 44382

Looks very neat!

Quote:

---

Originally Posted by Trevor Davies

Looks very neat!

---

Cheers, much appreciated!!!

Update:


Some more parts I ordered from Evatco just arrived in the post, the black caps are F&Ts, blue caps are Sprague Atoms:

Attachment 44398

Any more thoughts on making a load bank? Don’t forget that if you put them in an enclosure you’ll need to have a lot of ventilation for them as they will get pretty hot. And unless they are being screwed to a heat sink, then they will need to be mounted away from any backboard/PCB for better heat dissipation.

9 ohms won’t make a difference compared to 8 ohms. A speaker impedance will be less at some frequencies and higher at others. If you want 8 ohms, just add some more resistors in parallel.

I’d certainly have more power capacity in the resistors than you need. I don’t know how close to its limit a 5W resistor passing 5W is, but if you give it more power when setting up the amp, then you could get a succession of blown resistors and no load bank, and power tube and output transformer damage following.

Of course you don’t need to bias the amp at full power with a signal going through it at all. Just use the speaker and don’t have anything plugged in the input.

Quote:

---

Originally Posted by Simon Barden

Any more thoughts on making a load bank? Don’t forget that if you put them in an enclosure you’ll need to have a lot of ventilation for them as they will get pretty hot. And unless they are being screwed to a heat sink, then they will need to be mounted away from any backboard/PCB for better heat dissipation.

9 ohms won’t make a difference compared to 8 ohms. A speaker impedance will be less at some frequencies and higher at others. If you want 8 ohms, just add some more resistors in parallel.

I’d certainly have more power capacity in the resistors than you need. I don’t know how close to its limit a 5W resistor passing 5W is, but if you give it more power when setting up the amp, then you could get a succession of blown resistors and no load bank, and power tube and output transformer damage following.

Of course you don’t need to bias the amp at full power with a signal going through it at all. Just use the speaker and don’t have anything plugged in the input.

---

Yep, I'm going to use the same type of metal enclosure as I used for my XR2206 Function Generator, it does have some good ventilation, and I'm also going to include a small 12V DC powered fan as used in some computer cases to add some extra cooling, with the help of another forum member, I came up with a suitable design for the Dummy Load that uses a total of X22 180 Ohm/5W ceramic resistors in parallel to give an 8.2 Ohm/110W Dummy Load, that should be more than enough for testing purposes.

Here's a link to the Dummy Load project thread I started:

https://www.buildyourownguitar.com.a...ad.php?t=12363


Note that the basic design I came up with can be easily modded to suit the requirements of those wanting to build one for themselves.

Update:

Thought I would post some more pics of the insides of my diy scratch-build Sloclone 50 amplifier, so here we go:

Attachment 44481

Attachment 44482

Attachment 44483

Update:


Just got these in the mail this afternoon, they are a couple of Dual 200uF/500V Can Caps I ordered recently from SoundLabs Group.com, I was a bit concerned that their diameter would be smaller than the two original blue LCR dual 50uF/500V can caps I had installed in the chassis, but turns out these are the same exact diameter as the LCRs, so, that means I can re-use the original chassis mounting-bracket hardware and I don't need to go to the trouble of ordering new mounting brackets.

Here's a pic of the new can caps:

Attachment 44502