Jam night amp ideas. Grab and go head

[tristanc]

I’m looking for some ideas for an amp for use at a local blues jam night. This is in a pub walking distance from my house, so I’d like to be able to carry all my gear and be self-sufficient as far as possible.

- light and compact
- medium gain - crunch without needing pedals
- master volume
- no more than 20W I reckon

It will be paired with an extremely lightweight Barefaced 1x10 or 1x12 cabinet (5kg).

I currently use my AX84 October (6V6) head and it’s running nowhere near full volume. But it’s in a heavy cabinet and perhaps overkill for the situation.

Which gave me the idea of modifying an existing build I have to have a bit more output: a small PP ECC99 circuit running at ~260V with 2x12AX7s + SS cathodyne in a 9x7x2” Hammond chassis. This amp doesn’t cut it at all in the same setting. Just too broken up.

So my current thinking is to:

• replace the ECC99 with a pair of EL84s (basically make a new preamp hole in the chassis and move everything over by one).
• replace the OT (I’ve a Hammond universal PP to hand)
• give the existing PT a go to see if it copes. If not, I’d get a beefier toroidal to replace that.
• make a simple pine box from off-cuts to put it in

That would maybe get 10W-15W depending on the voltage?

Or am I barking up the wrong tree and should just get a Princeton?

[rake]

Doug's 18w Stout may do the trick
Single 12 or a single 10 with a minimal cab?

https://el34world.com/projects/images/18WattStoutReverbSchematicNoSwitch.gif

[passaloutre]

I use a 5E3 combo for a similar local jam night. Plenty of crunch at a level appropriate for drums and a weak vocal PA. I put together a 3/4" pine cabinet with a 12" Jensen and it's the lightest amp I own.

[tubeswell]

5E3, 6G2 or 6G3

[Willabe]

Princeton Reverb with a 12" speaker and option of using a Deluxe Reverb OT in it, or single channel Deluxe Reverb.

[TIMBO]

Hey mate, Check out this one
Marshall 2144 Combo (el34world.com)
You could sub the tank reverb with the belton brick

[bmccowan]

Of amps I've built, 6G2, 6G3, Plexi6V6, and a Mojo NC3015 modified for 6973/6CZ5 power tubes. All were built as heads except the 6G2 which has a 12" Weber. I now wish I had built that as a head too. I'm interested to hear what you decide.

[Platefire]

 What I use is my slightly modified Pignose G40V. The cabinet is smaller than my DIY Champ but has the power of PP 6L6 witch is mainly a 5F6A bassman circuit with MV and extra gain stage. My modifications were to remove the extra gain stage and revise the speaker bafflefor a 12" speaker. It's definitely grab and go---guitar & gig bag in one hand, amp in the other.

[tristanc]

Thanks for all the ideas and pointers.

What I'm going to try is a quick and dirty modification / rebuild.

3 stage + CF in to a SS Cathodyne PI, in to a 2x EL84 cathode-biased PP power section. Scheme attached.

I managed to source a new PT that should get me ~325Vdc, and is only a tiny bit bigger than the current one.

So it's a case of punching out an additional noval socket hole, and moving things about in / on the chassis to make it all fit.

I'm also planning to switch tone stacks from CF-driven 2 knob Bone Ray to a CF-driven 2 knob Bandmaster style. Basically this will change the preamp to be closer to Merlin's Medium/High Gain design in his book. If there's room I may try to add the interstage mid control (the pot may need to be on the rear).

It won't be pretty, but hopefully gets me ~10W.

[acheld]

I carried my buddy's Revv D20 out to the car last night before listening to his gig.  Amazed at how light it was, yet was able to punch through the band.

Anyone have a schematic for this? (I can't find one, and my friend won't let me tear his down).   I'd love to build one minus all the digital doodads it has -- as best I can tell, it is reminiscent of a DR, but small and light weight.

[pullshocks]

I'm also planning to switch tone stacks from CF-driven 2 knob Bone Ray to a CF-driven 2 knob Bandmaster style. Basically this will change the preamp to be closer to Merlin's Medium/High Gain design in his book. If there's room I may try to add the interstage mid control (the pot may need to be on the rear).

Have you tried the Bandmaster style tone stack before?  If not, be prepared for some wierd response as the controls are turned up.    I thought at first I must have made a wiring error, but it was wired per Merlin's schematic.  The effect can be seen with the Tone Stack Calculator In the Web.


I'm not saying you shouldn't try it--it does its job through most of the control range.  And I think the Merlin Medium Gain preamp sounds great overall

[tristanc]

Have you tried the Bandmaster style tone stack before?  If not, be prepared for some wierd response as the controls are turned up.    I thought at first I must have made a wiring error, but it was wired per Merlin's schematic.  The effect can be seen with the Tone Stack Calculator In the Web.

I'm not saying you shouldn't try it--it does its job through most of the control range.  And I think the Merlin Medium Gain preamp sounds great overall

I haven’t as yet - I’ll have a go at simulating it in LTSpice. As it happens, the pots I needed didn’t arrive for this weekend’s blitz, so tone stack changes will have to wait.

As for the blitz, I had 6 hours to get something workable. I used what parts I had lying around from previous builds and just bodged things together as best I could in the tight space. Not pretty at all. Not suitable for years on the road. But it will do for now.

I've switched it on, biased the EL84s to 11V, and it passes sound (and good ones too) apart from some heater hum that shouldn't be there... So I've messed up somewhere.

I doubt anyone can help scan the images for any heater wiring faults given the mess. I just hope it isn't the proximity of one EL84 to the PT.

[tristanc]

I've switched it on, biased the EL84s to 11V, and it passes sound (and good ones too) apart from some heater hum that shouldn't be there... So I've messed up somewhere.

After trying numerous other things (repositioning screen resistors, rerunning some heater wiring, reflowing joints, chopsticking etc etc) I narrowed things down by clipping additional caps in parallel to the first couple of filter caps. Doing this to the screen decoupling cap (47uF with another 47uF) made a big difference. Then I realised the dropping resistor was only 100ohm. Upping this to 4.7k got rid of the hum. I may replace it with 1k as the voltages to the preamp drop a bit, along with pushing the B+ up a bit to 340V

Will be using the amp tomorrow night. Fingers crossed it survives!

[tristanc]

I very hastily assembled a headshell, and took the amp to the jam night.

The total package is 4kg, so perfect on that requirement.

It kept up with a Deluxe Reverb, and sounded great even through a 1x12 Blues Jr Cabinet (boxy).

So I'll take that. Further changes to the tone stack (Bone Ray -> Bandmaster after the CF + a mid control after the 2nd stage) and some tweaking of the bias and dropping resistors to follow no doubt. And some 'scoping to measure the output and check there isn't anything strange going on. Oh, and tidy up the headshell with a router + round over and a coat of varnish.

[tristanc]

Have you tried the Bandmaster style tone stack before?  If not, be prepared for some wierd response as the controls are turned up.    I thought at first I must have made a wiring error, but it was wired per Merlin's schematic.  The effect can be seen with the Tone Stack Calculator In the Web.

I'm not saying you shouldn't try it--it does its job through most of the control range.  And I think the Merlin Medium Gain preamp sounds great overall

I see what you mean… I had exactly the same reaction - “must be a wiring error” - which was partially true: I had the bass control wired backwards. Fixed that and still felt both the range and interaction very strange. Some tweaking of the following gain control is needed at certain settings to counter the signal loss.

The middle control (from the High Gain design) is interesting too. I’m playing with this in LTSpice to see if what I hear is backed by simulation. With the Bandmaster stack bypassed and using only the middle control I get some great tones, clean and distorted. Switching in the stack takes quite a bit of tinkering to get the sound in the zone.

I used the amp for another jam session this week - opinions varied. Potentially the Bone Ray was better… Will take time to get used to it.

[pullshocks]

Thanks for the update.  I'm looking at Merlin's book section 11.6 about the mid control, what setting did you like?


As far as the "Bandmaster" tone stack, it was reassuring to me that you also  found it a little strange.  Due to hearing loss issues and hearing aid idiosycracies, it is often hard for me to judje amp sounds.  Fender-like clean sounds are still great, but finding overdrive tones that sound consistently good is elusive.

[Willabe]

I'm looking at Merlin's book section 11.6 about the mid control, what setting did you like?

Fender amps with no mid control use a 6K8 R to set the mids in the TS. That's like setting the 10K mid pot on ~ 5 or 6. So that should give you an idea of where you at with a mid control in a Fender amp. 

[tristanc]

Here are a couple of sweeps of just the tone stack drawn in Merlin's book, Chapter 11.

One is increasing both controls in 0.05 steps between 0 and 1.

The other is increasing Bass from 0->1 whilst decreasing Treble from 1->0 in 0.05 steps.

Interesting to see how the mid scoop develops as both controls are increased. And how the response is flat near 0.

I'll do the same for the circuit I've used later tonight.

EDIT: for completeness, a 3rd plot of both controls varying: 0, 0.5, 1.

[tristanc]

Have you tried the Bandmaster style tone stack before?  If not, be prepared for some wierd response as the controls are turned up.    I thought at first I must have made a wiring error, but it was wired per Merlin's schematic.  The effect can be seen with the Tone Stack Calculator In the Web.

I'm not saying you shouldn't try it--it does its job through most of the control range.  And I think the Merlin Medium Gain preamp sounds great overall

The middle control (from the High Gain design) is interesting too. I’m playing with this in LTSpice to see if what I hear is backed by simulation. With the Bandmaster stack bypassed and using only the middle control I get some great tones, clean and distorted. Switching in the stack takes quite a bit of tinkering to get the sound in the zone.

I used the amp for another jam session this week - opinions varied. Potentially the Bone Ray was better… Will take time to get used to it.

Reporting back on this build. I have ended up replacing the Bandmaster Stack with the Bone Ray! It just seemed to 'work better' for me. I've simulated both and it should be possible for both to cover the same ground, but for some reason the Bone Ray just works. I altered the values from Merlin's book to work for the 500k pots I had to hand, then altered a couple of cap values to tweak the position of the mid cut.

What's interesting (to me) is to understand the utility of having the two middle controls (one early and one later) in the signal chain.

• The 1st mid control seems to operate as a gain control and at lower settings gives less distortion and more mid scoop (perhaps a more Fender-y sound?). At higher settings or full it's basically out of the circuit.
• The 2nd mid control means an even bigger scoop (too much) or, put up high, gives a 'fuller' sound when the 1st control is low.

So interesting interplay between them.

One further mod I may do is to replace the 33k resistor to ground in the mid filter with 50k to shift the position of the notch ever so slightly and perhaps decrease the attenuation immediately after the filter. Likely not noticeable, but I can't leave things alone.

Latest schematic and source: https://github.com/tristancollins/Guitar-JamNight
Also attached.