Hiwatt Custom 50W Amp excessive rectifier buzz in output

[Helmholtz]

...or is it perhaps an issue with the current rating specified in the products' power xfmr, not allowing for sufficient current to run the heaters in the power xfmr?

The clipped heater voltage tops are not related to the heater current. It's not a saturation effect.
You should see them on the no-load heater voltage as well.

Rather they are caused by the clipped HT voltage and transformer coupling.
A larger PT having lower primary DCR will show less clipping.

But the nasty spikes are not caused by the clipped tops themselves, but by the sharp voltage drop on the trailing edge of the clip.
This effect is related to energy storage/release in the leakage inductance of the transformer.

So a PT having less leakage and lower primary DCR is less likeky to cause large spikes.

Of course a separate heater transformer will not suffer from the effect at all.

[nevetslab]

NOW THAT (in the first image) is what I'm looking for! Far superior to the flimsy spring wire most mfgr's are using. Never cared for the stupid clamp found the Fender Blues Junior. Those springs are SO easy to lose if they don't attach themselves to the magnet when they pop out. Did you add the red rubber O-Rings in this setup? Nicely thought out. I'll pass this along to Hiwatt, as THIS is far closer to their fine build quality!!

Thanks,

Steven

[Pedro Vecino]

Yes, I add the rubber rings. One of them embedded in the end as it helps to center the support on the tube and provides some damping. In fact, I see them wide for EL84.

[nevetslab]

Yes, I add the rubber rings. One of them embedded in the end as it helps to center the support on the tube and provides some damping. In fact, I see them wide for EL84.

I ordered a set of the clamps this afternoon, and will see what I can do with my hi temp silicon rubber tubing that I normally use on the larger hold-down clamps. The smaller tubing I use looks like I can slit it to work into the hole in the 'hat' to serve as a grommet on the top of the tube. In your photo, the springs look like they're very taut from being stretched a lot. I'll have to play with that. I'll see how the other tubing size I use works on the fingers to center the tube. If need be, I might try the small dia shock cord I use on condenser microphone shock mounts instead of the springs. I'll post the results after I've played with them.

[nevetslab]

The Belton 50703 Hold-down clamps arrived today, so I sat down with those, cut some of the 3/32" ID hi temp silicon rubber sleeving to the circumference of the hole in the hat (1.85" long), slit it and rolled it into place, so that fits nice and snug, seating the top of the EL-84 tube. I used the 3/16" ID hi temp sleeving to fit onto the four fingers of the clamp 'hat', making the two with the springs a touch longer to cover up the spring/finger joints. Bent the four fingers in a touch so they'd cradle the sides of the tube.

I had a collection of the mounting flange that is received with the new thin spring-wire hold-down clamps that everyone uses, put a 3/32" Taper Pin Reamer into my small tap wrench and opened the upper holes of the two mounting tabs for the spring wire clamps, just large enough for the Belton hold-down spring clips to pass thru. Installed a tube socket to the assembly to install an EL84 tube and took a look at the results.



The mounting flanges that come with the spring wire clamps is thin metal, and I suspect trying to open them up with a 3/32" drill may be a problem. Not so with the smallest taper-pin reamer I had. It did leave a burr, but that worked well getting the clip thru the hole. I had to use needle-nose pliers to hold the clip open to slip it thru the hole.



I also thought of using a short threaded #4-40 standoff or male-female #4-40 stud-standoff, with a a Keystone right-angle bracket or solder lug....still would have to enlarge the hole for those tiny clips to pass thru.

Now, I need to get the Hiwatt Little Rig back here to the shop, as those have now gone into our rental inventory from Hiwatt.

The Hi Temp Silicon Rubber tubing.....the inside hole of the 'hat' uses 3/32" ID, 7/32" OD, P/N 3038K12 (10ft length), and the spring/tab & wings use 3/16" ID/5/16" OD, P/N 3038K14. McMaster-Carr. https://www.mcmaster.com/catalog/127/159/