18Watt.com

I hope it's ok to talk about ceriatone amps here. I posted there, but didn't get any answers. Looking at the layouts, the 18 watt and the 20 L&B seem to use the same power transformers. Input can be 120 or 240V, and output is 290 or 3.15 V. I'd rather not have a heavy transformer shipped from abroad, when I can get one in the US. Looking at the Mojotone site, which is the distributor (I think) for the Heyboer transformers, they have a transformer for the 18 watt that has outputs of 290 (two of them) and 6.3 (one of them) volts. Would this transformer work? 3.15 is half of 6.3, so maybe I'm just looking at the specs wrong. If this won't work, can anyone recommend inexpensive but high quality transformers readily available in the US? I'd rather not spend $ on a MM transformer.

As a second question, is it possible to build this amp as is, but with an additional jack to bypass the preamp, so that I can use other preamps with it?

Thanks

Yes that mojo power tranny is the Heyboer that works for 18 Watters, model HT 6179. I used it for my Denim Deluxe.

Thanks for the reply. What's the deal with the 6.3V tap? Upon looking further at the spec, it looks like the 6.3V tap goes ONLY to the pilot light. Is this correct?

Also, I don't see the output transformer in the specs. What am I missing?

Thanks

Layout: http://www.ceriatone.com/ceriatone/wp-c ... pt2018.jpg

I'm not familiar with that amp but I would cross reference the layout with the schematic. Usually the pilot is on the filament line.

You're right, I missed that. The lesser voltage tap feeds the filament. Since the filament voltage is greater in the Heyboer, wouldn't the gain be less?

For example, in one circuit:
"The actual gain that may be achieved in a voltage amplifier increases. Increases in gain of 1.5 times have been measured when the filament voltage was decreased from 6.3 volts to 3.0 volts."
Source: https://ieeexplore.ieee.org/document/6811062

On the layout F1 and F2 (F for filament) are the supplies for the heaters. You will see them at the valve bases as well as the pilot light. Considering how wiring the heaters can cause issues for inexperienced builders, I think that is not very helpful. I would expect the heater runs to be shown twisted and run along the periphery of the chassis because that matters. Maybe that is covered elsewhere in the kit instructions?

Dd

Edit: Sorry your post arrived while I was writing mine. One has a centre tap and one has not. So the voltages look different but are both the same to the heaters when wired up.

To clarify, there isn't only one distributor for Heyboer. There are multiple, and each version has their differences. Sonically I'm sure they're all probably comparable, but there are some differences. I prefer the GDS custom Heyboers because the PT has solder lugs instead of wires. This is ideal because you're not limited to the leads that come with the iron.

For example, ZP suggested I try elevating my heaters on a design I'm working on. So I desoldered the CT lug, and ran a new wire to the cathode of the power tubes. My heaters were so quiet it didn't make a difference, so I desoldered and switched it back to normal. I wouldn't have been able to do all that with the other versions of the PTs, and I would have been stuck experimenting with extending wires or terminal strips, neither of which is as good (or as pretty) as a single wire done properly.

Edit: you can get the GDS version from GDSAmps.com - Graydon was one of the founding members of this site.

Awesome, thanks for the replies.

Bionic_Bigfoot wrote: ↑

Tue 08/06/19 11:38 pm

Also, I don't see the output transformer in the specs. What am I missing?

The layout shows the inside of the chassis. The OT is mounted on the outside (or possibly externally - some old designs had them on the speaker frames). Pins 7 of the output tubes show the blue and brown leads to the OT. The red wire to that 10W resistor labeled "OT CT" is the OT red center tap wire.

Got it, thanks.