36 watt build - at least it doesn't squeal

[George61]

My first guitar amp build was a 36 watt Ceriatone kit, AKA the hum-hiss-squeal-fizz master. My second build was a Rocket clone, which works good, so I decided to take a shot at re-building the Ceriatone. I decided to try a slightly different design so I got a turret board, from Watt's Tube Audio, for the Richie Hall 36 watter on 18watt.com.

The amp is finished and it works pretty good. Even with everything dimed it is resonably quiet. The Rocket is definately the superior amp. The 36 watter bass is muddier and the highs are a bit harsher compared to the Rocket. Some of that may be the Sozo capacitors which, from what I've read, need an extensive break-in period. At least the amp doesn't squeal and it's purty.

Solder on,
George

[xtian]

Can't fault your lead dress. Looks beautiful!

The Rocket has a lot more filtering, which helps stiffen bass response.

[Colossal]

Your build quality and part choices are exceptional. What rectifier are you using? NOS or new production. Which brand and type? The Sozos do require break in but you should have a very clear sound but not muddy per se. If anything too trebly at first and mellowing into a clear and shimmering midrange roar. What value grid resistors did you use on the EL84s? What is the bias point and plate voltages on this amp?

[George61]

Your build quality and part choices are exceptional. What rectifier are you using? NOS or new production. Which brand and type? The Sozos do require break in but you should have a very clear sound but not muddy per se. If anything too trebly at first and mellowing into a clear and shimmering midrange roar. What value grid resistors did you use on the EL84s? What is the bias point and plate voltages on this amp?

The rectifier is a new production Sovtek 5AR4. Grid resistors are 8K2 as per the schematic. Plate voltage is 345 vdc on EL84's and the cathodes are 11.9 vdc.

Since my origianl post I played around with the amp. I swapped the JJ EL84's for my 6P14P-EB's which was an improvement.

The amp is an odd design. The 'Tone' channel and the 'TMB' channel are both fed the the grid of V2A. That makes the cathode follower and TMB controls in effect on the tone channel but the TMB stack is defeatable. This arraingement leaves one side of the PI free and the negative feeback is fed to that. On the origianl design the negative feedback was fed to the tail of the PI and had almost no effect but on the Richie Hall design the negative feedback has a drastic effect, it relly tightens up the amp. The negative feedback is switchable. With the negative feedback in and playing around with the bass, middle , treble controls I can get a sound that I like a lot and if the amp mellows out with age it will be a really nice amp.

The bass is not gawd awful with negative feedback off, but it is boomy, muddy enough that I find myself avoiding the low E string on the guitar. My main guitar is a Jackson Dinky with dual humbucker pickups.

[Colossal]

The rectifier is a new production Sovtek 5AR4. Grid resistors are 8K2 as per the schematic. Plate voltage is 345 vdc on EL84's and the cathodes are 11.9 vdc.

Spot on. The Sovtek is great and the best of new production 5AR4/GZ34s IMO so that helps eliminate that as a source or contributor to the mud.

Since my origianl post I played around with the amp. I swapped the JJ EL84's for my 6P14P-EB's which was an improvement.

I have the same Russian tubes (and like them a lot) but what did or didn't you like about the JJs (more of an aside question, not so much as pertaining to a possible contribution of mud)?

The amp is an odd design. The 'Tone' channel and the 'TMB' channel are both fed the the grid of V2A. That makes the cathode follower and TMB controls in effect on the tone channel but the TMB stack is defeatable. This arrainge ment leaves one side of the PI free and the negative feeback is fed to that. On the origianl design the negative feedback was fed to the tail of the PI and had almost no effect but on the Richie Hall design the negative feedback has a drastic effect, it relly tightens up the amp. The negative feedback is switchable. With the negative feedback in and playing around with the bass, middle , treble controls I can get a sound that I like a lot and if the amp mellows out with age it will be a really nice amp.

The bass is not gawd awful with negative feedback off, but it is boomy, muddy enough that I find myself avoiding the low E string on the guitar. My main guitar is a Jackson Dinky with dual humbucker pickups.

Would you mind posting a schematic if you have one and if you are ok with it. I know I've seen Richie's schematic before but I don't think I have it. I've posted what I have in the 36W Marshall family and it does not match the feedback circuit you are describing.

[Firestorm]

Spot on. The Sovtek is great and the best of new production 5AR4/GZ34s IMO so that helps eliminate that as a source or contributor to the mud.

Sorry for the hijack, but how good are the new 5AR4s? I am so addicted to NOS Mullards that my vision is clouded.

[George61]

Would you mind posting a schematic if you have one and if you are ok with it. I know I've seen Richie's schematic before but I don't think I have it. I've posted what I have in the 36W Marshall family and it does not match the feedback circuit you are describing.

The schematic is after all the pictures in my original post - 36wTMB5.pdf.

As far as the Russian tubes go, I think they are a little more defined (pristine?) and have a bit more clean headroom than the JJ's. I grew up in central Pennsylvania in the 60's and the area was a hotbed of Jazz and blue-eyed soul. I tend to lean towards cleaner, less distorted guitar tones.

[Phil_S]

The 18W folks call it heresy. If you want more clean headroom, change the 470K grid leak resistors for the power section to 220K. That will crank down the Marshall vibe some without totally neutering the amp. If you want to do a non-invasive test, simply tack another 470K over the existing pair in parallel, making 235K and see if you like it.

[George61]

The 18W folks call it heresy. If you want more clean headroom, change the 470K grid leak resistors for the power section to 220K. That will crank down the Marshall vibe some without totally neutering the amp. If you want to do a non-invasive test, simply tack another 470K over the existing pair in parallel, making 235K and see if you like it.

Check out the schematic. It is designed with 330K grid leak resistors. The PI plate resistors are 68K and 82K. I believe that gives the PI considerably less gain than the standard 470K and 100K design. The amp still has lots of distortion. With the negative feedback in (another no-no?) the amp starts to break up with the master at 10 and the volume at 4.

[Colossal]

Sorry for the hijack, but how good are the new 5AR4s? I am so addicted to NOS Mullards that my vision is clouded.

I have and am spoiled on NOS Mullards as well and they are my benchmark standard. I find the Sovtek 5AR4 to be a remarkably close second to the sound and feel a real Mullard provides. It is a great sounding tube. The JJ GZ34 is rather pedestrian sounding to my ear.

[Phil_S]

The 18W folks call it heresy. If you want more clean headroom, change the 470K grid leak resistors for the power section to 220K. That will crank down the Marshall vibe some without totally neutering the amp. If you want to do a non-invasive test, simply tack another 470K over the existing pair in parallel, making 235K and see if you like it.

Check out the schematic. It is designed with 330K grid leak resistors. The PI plate resistors are 68K and 82K. I believe that gives the PI considerably less gain than the standard 470K and 100K design. The amp still has lots of distortion. With the negative feedback in (another no-no?) the amp starts to break up with the master at 10 and the volume at 4.

Not on the PI. I'm talking about the pair of 470K grid leak resistors for the EL84's. They appear on the schematic post PI, after the .022 coupling caps and before the 8.2K grid stoppers.

On your photo Gut 2, these are at the lower right side, an inverted V with a wire in the middle going to the ground buss. (I can't make out the color stripes, but they should be 470K if built to spec.) There is red wire coming from one to the grid stoppers on the right pair of power tubes and a white wire off the other to the grid stoppers on the left pair of power tubes.

The grid leak change will give you more clean headroom in the power section.

Now, if you want to Fenderize the PI and goto 100K/82K go right ahead. It's your amp!

If you don't have the NFB switch, just break the connection and jumper the 56K tail resistor to ground for a test.

[Structo]

Great looking amp!

Nice job!

[dougfret]

Currently building a 36 watt Richie hall looking at layout from 18 watt. com I believe in stall power trans has a 55vac bias tap ? could use some help if it possible to hook up or should I just get another transformer ?

[martin manning]

The layout shows a cathode bias arrangement, so you don't need the bias tap. What about the rest of the transformer specs? Does it have a 5V 2A winding for the rectifier filament? 290-0-290 HT?
Schematic: http://mhuss.com/18watt/schematics/

[Richie]

A few things about the amp and different layouts and schems. Over the years, Some things depending on the layout etc, have been changed,or were never corrected. And some have added their own take on the amp.

One important one to keep the bass more adjustable, is changing the .022 cap in the tone circuit, to a .01.

And the other is to make sure the feedback circuit is correct. I think both are incorrect on ceriatone.

Also might change the tone slope to 39k.

Some show some differences in the PI values, and the input to V2 from the volume pots.

I still have my proto type amp here. I may have to open it up to see what is in there..

Some people don't realize that if you are in the normal channel, you have a tone control, but also the TMB controls work for that channel. So you can fine tune that channel too.
Or the bass control has a Tone bypass mod that lifts those controls. And the Normal channel is more 18 watt like then, and must have the feedback flipped out. If the feedback is in, it will make the normal channel very wimpy and not like an 18 at all.

The feedback circuit is more for the TMB channel,or marshall like channel. But it can be used either in or out depending on what your wanting. You can get more clean with it in.

Their are other ways too, if you didn't want the channels to sum together, then you could sum them at the PI. Similar to a fender amp. And could also use a Lamar MV.

Their use to be a tweak sheet. But basicly most marhsall mods that are out there will work.