18watt Cascade preamp layout

[distortionhead]

Hi guys, building my first tube amplifier . Thought of building the 18watt with the cascade preamp. Drew out a layout for it from the modulus 18watt single channel layout. Can someone point out any issues or mistakes (which there will be) .

[Willabe]

We need a schamtic to go with it.

We use the schamtic to cross check the layout.

[distortionhead]

  posted

[tubeswell]

Not a fan of that parallel/cascade switching method. The contacts on the pole that is switching to the plate would tend to arc with switch bounce. YMMV

[distortionhead]

Not implementing the switching . Permanent cascade preamp

[Willabe]

Ok, but that's only the preamp, need the whole amp's schematic also.

[distortionhead]

It's a preamp mod for the 18w

[bmccowan]

Not implementing the switching . Permanent cascade preamp

Isn't that what the Hoffman Stout is?

[distortionhead]

In the stout isn't the volume and tone after the first stage ?

[tubeswell]

Not implementing the switching . Permanent cascade preamp

Isn't that what the Hoffman Stout is?

The schematics posted at the start indicated otherwise - but hang on while I grab my crucifix to ward off evil

[bmccowan]

In the stout isn't the volume and tone after the first stage ?

Yes it is. I guess I should have been clearer that I was referring to the extra gain stage vs the parallel V1. Which topography (tone stack location) offers the better control? -  Have many of the circuits you posted been built? Results? Would be pretty easy to change the stack insertion point and seeing what you like.
IMO, 18Wers with too much gain sound like crap. But I've aged out, so probably best to ignore my opinion on that.

[distortionhead]

Yes the stout looks like the cascade preamp baring some value changes. Needed a MV , replacing the 470k to ground after the 2nd stade seems to be the location. Also I'll be using solid state and don't have a choke for the power supply. What would be the things to note about the change?
The PT is 0-275v , rectified gives about 380v after rectified.

[bmccowan]

380V on the EL84s should be fine. Dropping resistor rather than a choke should be fine. I think plenty of 18W variants are consistent with that. Neither will have a large effect on tone, IMO.
BTW, I'm not suggesting you build any particular variant of the 18. There is a whole world out there.
My comment on high gain 18W amps comes from building an 18TMB a few years ago. The TMB channel is high gain and I ended up taming it down a lot. Even then I liked the normal channel better. But that's just a preference thing. Others here and elsewhere will likely and have more experience with high gain amps, including the 18.

[distortionhead]

It's my first amplifier build, so looking for something simple. It's getting build from an old pa amplifier I found. Wanted a MV for keeping it down. That's how I found the 18w cascade mod preamp.

[bmccowan]

It's getting build from an old pa amplifier I found

That's a fun way to go. Would be good to share what you have for a PA. There are not many old PAs with EL84s. Is that where you are starting from?

[distortionhead]

It's getting build from an old pa amplifier I found

That's a fun way to go. Would be good to share what you have for a PA. There are not many old PAs with EL84s. Is that where you are starting from?

These are a few I have one is a pushpull EL84 based pa amplifier another is a quad push pull , also have one with 3 pairs in the output section , Iam from India ,most of the pa amps I have seen are EL84 based, we had a manufacturer with Philips and mullard machinary back in the day BEL . Also have a few more in my collection.

[bmccowan]

Cool - well that explains the EL-84s. I don't suppose you have a schematic? I see there are some youtube vids on these amps.

[distortionhead]

I do have the schematic. The ones I showed are for a future project a friedman 20watter, pink taco. Or a 6v6 jcm800 from robs site

[distortionhead]

Building on an different chasis I have , that's striped off everything

[distortionhead]

made some progress in wiring up the board and b+ and heater wiring, I know my soldering skills are not stellar , out of touch haven't build anything in a long while. posting some pics. question: I don't have the choke, what would be a good dropping resistor in its place, thinking of a 1.5K 10W , looking at other schematics, Iam getting 380V unloaded at first filter cap after rectification. That's like 10% higher than mentioned, it shouldn't be an issue right? 

[tubeswell]

I don't have the choke, what would be a good dropping resistor in its place, thinking of a 1.5K 10W , looking at other schematics, Iam getting 380V unloaded at first filter cap after rectification. That's like 10% higher than mentioned, it shouldn't be an issue right? 

Try 1k and minimum of 20uF filter caps at the 1st and second place power supply nodes, and be prepared to increase filter capacitance if ripple hum is present. The wattage doesn’t need to be excessive.

The voltage should drop somewhat when you plug tubes in.

[distortionhead]

First node is 47uf then Im using 22uf in successive nodes.

[distortionhead]

Wired up the board into the chassis, waiting for a couple of things to arrive. will check and post voltages.

[dmp]

Once you have it built and working you can swap around the stages pretty quickly to hear how it sounds. Can try v1a->TS->v1b or v1a->v1b->TSDifference is whether the tone stack affects the signal before it is sent through the overdriven gain stage or after.Just be sure to build with separate cathode resistors on v1 instead of the shared 820R.
I just am finishing up a 18 watt build and playing around like this.
The stout design is really great as is the straight 18w Marshall.  Different flavors.
Many ways to change it around once you have it working: feedback or not, cathode bypass caps, etc...
You can use a pot for the 470k after v1b or use a master volume after the PI. Or an attenuator after the OT. Different ways to do it.

[distortionhead]

yes thinking of a few mods, definitely will add a 500k pot after v1b, add a bypass cap to v1b , make the feed back switchable.

[distortionhead]

made some value mods , the v1a bypass cap is a .68uf and added a 100uf bypass cap for v1b ,powered it up through a 100W light bulb , measure the voltage , the voltages where
Node A 280V Node B 264V after the 1.5k resistor used in place of the choke Node C was 247V Node D was 240V, the bias voltage was around 7.6v , the bias resistor is a 150 Ohms instead of 130 Ohms. I'll post a detailed voltage chart later.