My first valve build for fifty years! Vox AC15 (1960 version) - Sound Clips!

[DLPublic]

This is my first post here, so by way of an introduction...

Back in the late sixties, I built a couple of valve transmitters, but finally got swayed by transistor (and later IC) technology as it made for simpler builds, no power supplies to build first, etc.  My other hobby was music and I played in 'pop groups' back then as well.  I retired just over 10 years ago, so was able to get back into playing the electric guitar again using a guitar I made in my teens that had been up in the attic for over 40 years.  Having always been an avid DIY'er, a few years ago I made a Hank Marvin (of the Shadows) replica Strat from scratch (not a partscaster as I also made the body, neck(s), truss rod(s), etc. as well) - see my avatar.  More recently I have built numerous FX pedals (Fuzz Face, Big Muff, Dyna Comp, PowerBoost, PT80 delay and a dual Echo Base delay, and the pedal board).

I currently have a solid state practice amp (Marshall MG15FX) but really would like a Vox for playing The Shadows stuff.  I considered getting a AC15C1 but as usual I have opted to build one instead.

After much research I have decided to build an AC15 based on the 1960 schematic (in Stephen Grosvenor's book) complete with EF86 channel and tremelo, with a couple of small modifications, i.e. putting the tremelo depth control and speed potentiometer on the front panel, and possibly a rotary switch for the brilliance.  As I mainly practice at home, I will also be adding Amp Maker's VVR/VCB kit to the power stage.

The build cost is just a tad over £500 excluding Speaker and cabinet (which I shall also build from birch ply) and have started ordering parts.  Am undecided as yet as to which speaker to use.  Most would probably suggest a Celestion Blue, but not sure I can justify the additional £100, so am considering either the Green back or Cream back.  Should it be 8 or 16 ohm?

I will be making a Vox style chassis (from 1.2mm steel and 2mm aluminium) myself with a (yet to make) simple bending brake so I hope that goes well as it saves another £50 over buying one on fleabay.  All signal resistors in the preamps and tremelo section are going to be 2W carbon film (Kiwame ones, which purport to be quieter than metal film) with 1W carbon film everywhere else excluding the high wattage ones which are ceramic wirewound.  The transformers are on order (Vox AC15 vintage 60's from LivinginthePast).  I intend to order the valves from Watford Valves (Harma Retro).  It will be built using phenolic tag boards (which I purchased for £10.50) whereas using turrets would have cost around £30.

Currently, finalising chassis design in AutoCad and control panel in Photoshop (see attachment) and tag board layout (which will mainly follow the one in Grosvenor's book).

Will keep you posted.
Dave

[CraigB]

Sounds like a fun project!  Welcome to the forum...it is a super place to read up on topics of interest and see what other people are working on, and make friends with other DIYers around the world

If this is the output transformer you ordered, the specs show 8 or 16 ohm secondary, so you can use either.

http://www.livinginthepast-audioweb.co.uk/index.php?p=xfrmrvt1504

[sluckey]

That's an ambitious project. I look forward to following your progress.

Several members have built that amp, although using a Marshall style layout. We also did the trem and brilliance mods you mentioned. Our layout is quite different from where you are headed but you may find some useful info on this link, especially the clear schematic...

     http://sluckeyamps.com/VAC15/ac15.htm

[DLPublic]

Craig - yes it is and I realise it supports both, but I wondered if there was any preference (either from an audio or operational standpoint) which would favour one over the other.

Forgot to mention the non-polar capacitors which will be silver mica and mallory 150s (polyester) with one 33nF orange drop (polypropelene) as I was unable to source that value in the Mallory range.  Did consider orange drops throughout but the mallorys seem closer in appearance to originals.  Electrolytics are Sprague Atoms with a F+T 8+8uF can.  The 16+16uF can came from Modulus Amplification and is an own brand.

[CraigB]

That's an ambitious project. I look forward to following your progress.

Several members have built that amp, although using a Marshall style layout. We also did the trem and brilliance mods you mentioned. Our layout is quite different from where you are headed but you may find some useful info on this link, especially the clear schematic...

     http://sluckeyamps.com/VAC15/ac15.htm

Don't want to be a hijack, but that build is beautiful work Steve!  Your website is awesome

[DLPublic]

Sluckey,  having trawled t'internet on the subject for weeks I have already seen your build (well done by the way) along with many others.  Another one I came across was at http://members.ziggo.nl/jheijer/AC15.htm, who incidentally also plays Shadow stuff.

[CraigB]

Craig - yes it is and I realise it supports both, but I wondered if there was any preference (either from an audio or operational standpoint) which would favour one over the other.

Forgot to mention the non-polar capacitors which will be silver mica and mallory 150s (polyester) with one 33nF orange drop (polypropelene) as I was unable to source that value in the Mallory range.  Did consider orange drops throughout but the mallorys seem closer in appearance to originals.  Electrolytics are Sprague Atoms with a F+T 8+8uF can.  The 16+16uF can came from Modulus Amplification and is an own brand.

I wouldn't hesitate to use 16 or 8.  I don't think there's any audible or operational difference.  (I could be wrong there, not sure.) 

Personal choice would be 8 ohm...that way if you wanted to swap the original speaker out for another one, you could have the flexibility to use the original speaker with an amp that has only 4 and 8 ohm taps.

[DLPublic]

Craig, you make a valid point re getting the 8 ohm option.  Thanks and in the event no-one adds anything to the contrary that's the way I will go.

[Paul1453]

As I am learning, the ohm choice for the speaker is only part of the equation.

Many 8 ohm speakers have quite different frequency response graphs.
Then the room dimension/acoustics plays a part.

Most all of these considerations are personal subjective sonic preferences of the user.

But I know for sure, that there can be very distinct sonic differences in a broad range of 8 ohm speakers. 

I think you will have to make your choice based on price, or pay whatever they ask for the speakers that sound best to you. 

[tubeswell]

Great project. I love alnico blues. Go crazy with mustard caps and NOS EL84s!

[SoundmasterG]

I think that even with the added cost you will be much more happy with the sound of the Celestion Blue than any other speaker in the amp. They are a necessary part of the Vox sound.


Greg

[tubeswell]

Vintage voxs with mustard caps

[DLPublic]

Tubeswell - Go crazy with mustard caps and NOS EL84s!

I already have the Mallory 150s and according to this link http://mhuss.com/php/pix.php?p=MalloryYellow many think these are close to the "sound" of the old Mustard caps.

Your images above are very interesting as I have not seen a close up of the guts of a real vintage AC15.  Thank you.  Yesterday I started to draw up the tag board layouts (did not realise how big the 2W resistors are going to be!!!).

[Edit - turns out the 2W resistors were not that big at all.  I had used the 5W size, Duh!  Have updated the tag board layout.]

Aluminium sheet arrived yesterday along with valve holders and 1W resistors, switches etc.  Need the steel sheet and transformers to arrive to confirm final chassis design.   I am planning to test out chassis layout using thick cardboard first to hopefully prevent mistakes with the real thing. 

[HotBluePlates]

I already have the Mallory 150s and according to this link http://mhuss.com/php/pix.php?p=MalloryYellow many think these are close to the "sound" of the old Mustard caps. ...

The mustard caps are polyester dielectric, and the 150's are polyester dielectric.

"Orange Drops" are not a single cap type but a family of caps with the same/similar orange epoxy coating. There are at least polyester (192P, 225P) and polypropylene (75P, 716P) dielectric variants, maybe others.

[CraigB]

Tubeswell - Go crazy with mustard caps and NOS EL84s!

I already have the Mallory 150s and according to this link http://mhuss.com/php/pix.php?p=MalloryYellow many think these are close to the "sound" of the old Mustard caps.

Your images above are very interesting as I have not seen a close up of the guts of a real vintage AC15.  Thank you.  Yesterday I started to draw up the tag board layouts (did not realise how big the 2W resistors are going to be!!!).

Aluminium sheet arrived yesterday along with valve holders and 1W resistors, switches etc.  Need the steel sheet and transformers to arrive to confirm final chassis design.   I am planning to test out chassis layout using thick cardboard first to hopefully prevent mistakes with the real thing.

Looks good!

[DLPublic]

What size potentiometers do you guys use, 24mm or 16mm?  Are there any pros and cons for either size?

My ac15 build will take 24mm pots but I generally use 16mm ALPHA pots for my projects.

[DLPublic]

Project Update 1

After a couple of failed designs for a DIY sheet metal bending brake, I finally made one up to the job of bending the 2mm thick aluminium and 1.2mm thick steel (see photos below).

On Tuesday I decided to chase up the transformer delivery and was told it would probably be another two weeks (as they are hand made by one individual).  However, they arrived on Saturday so was able to start drilling the chassis.  Thought I would tackle the hardest one first, i.e. the power chassis, as this requires a couple of square cutouts (for the power and output transformers) and a 32mm circular hole for the dual capacitor can.  So far so good (see photos below).

One thing I only realised today is that the control panel is the opposite way round from what I expected.  Apparently, Vox designed the control panel when the amp was usually placed in front of the artist, whereas today, it is more likely to sit behind.  I did briefly consider turning it round, but decided to keep it as per Vox original.

Hopefully will drill the pre-amp chassis tomorrow.
Will keep updated with progress.

[Paul1453]

Looking good.   

That one is not a basic chassis.

It seems you have the skills to do it well.

I'll be interested in seeing your progress on this.   

[DLPublic]

Today's work is done.  Both chassis are complete and bolted together.   I have cheated somewhat on the second image by sticking a paper printout of the control panel!!!

[Ed_Chambley]

Nice Progress.  I really love my AC15.

[DLPublic]

Today I populated both pre-amp tag boards but I have a question.

I can see that a ground bus is used across the control panel between the input jacks and the channel I & II volume controls.  But how are the many ground connections on the tag boards wired?  Are they grouped in stages with each stage wired back to a single grounding point (i.e star connections from each stage) or are they all connected together with just a single connection to a common grounding point?

I have not come across an image that shows this detail and Stephen Grosvenor's book does not cover this aspect, it simply labels each relevant tag as 'gnd'.

[G._Hoffman]

I just finished my AC-30, and it's freaking awesome!


Gabriel

[DLPublic]

I just finished my AC-30, and it's freaking awesome!
Gabriel

Gabriel, perhaps you can answer my question (see reply #20 above) regarding how the various ground connections on the component tag boards are wired or at least how you did it in your build.

Dave.

[G._Hoffman]

I just finished my AC-30, and it's freaking awesome!
Gabriel

Gabriel, perhaps you can answer my question (see reply #20 above) regarding how the various ground connections on the component tag boards are wired or at least how you did it in your build.

Dave.

I do things a bit different from what is "traditional."  I spread my power resistors and my caps through the amp, so they are right next to the signal components they are related to.  Then, I use what someone (I believe it was Merlin) call's a "galaxy" ground.  All the signal grounds go to their related caps, and then all the caps go back to the "reservoir" cap (in my case, always two caps in series, with bleeder/balance resistors.)

I put up my schematic and layout in THIS THREAD OVER HERE.  (Be warned - I use a 13"X19" printer, so they might be hard to read on a smaller printer!)


Gabriel

[DLPublic]

Gabriel, many thanks for you input and the link to your schematic/layout.

I do things a bit different from what is "traditional."

So what is the traditional way?

I have followed the original layout so only the two 22kohm/5W (R4/R16) feeding the EF86 and phase inverter are on the preamp tag boards close to their filter caps (C4/C8) - a dual cap can mounted on the chassis.   I have grouped the tag board grounds by stage and am wondering whether I should connect each group to their logical point on the control panel bus.  I seriously do not want to suffer from hum in the final build so need to get this right.

Dave

[DLPublic]

update #2

Have completed most of the wiring so thought I would add some photos of the current stage of this build.

The steel chassis has been sprayed with an etch primer to prevent rust.  I have not connected the heater wiring to the transformer yet as I am considering using an inline fuse which can be accessed from the side of the chassis so that it can be inspected/changed without removing the complete chassis from its mounting board.  As the transformer does not have a centre tap for the heaters, presume I should create a virtual centre tap with two 100 ohm resistors.

I have wired the BRILLIANCE rotary switch in such a way that I can add additional capacitors to provide more options on this control.

The ground connections from each valve stage are connected to the ground bus (which is connected to the chassis at the input end) running behind the panel controls.

Just found out the supplier I am using for the speaker and valves is on holiday until later this month so unable to order these items until then.  BTW - I have decided to go with a Celestion Blue speaker.

So while I wait, I will start drawing up the cabinet details in Autocad.
Dave

[DLPublic]

As I had some 4mm silicone tubing lying around I thought I would use a couple of small slices to act as anti-vibration washers beneath the EF86 valve socket.  Hopefully this will reduce the chances of suffering from microphony effects.

[sluckey]

Looks nice.

[pompeiisneaks]

Wow, looks great!

[tubeswell]

Very tidy

[DLPublic]

Here is my initial AC15 Combo Cabinet design.

purple lines represent piping and blue lines represent the chassis.
I have added images of the speaker and faceplate (correctly scaled).
All the main dimensions are shown along with a cut list of materials.

The measurements are metric.  However, comparing my "Thick Edge" imperial dimensions against an original AC-15 1x12 "Thin Edge" cabinet as given by North Coast Music...

              Original      My design    Difference
Height:    20.75"          21.06"         +0.32"   (~8.13mm)
Width:     20.75"          20.276"       -0.474"   (~12.05mm)
Depth:    10.375"         10.827"       +0.452" (~11.5mm)

The top cutout for the faceplate is included, however, I have yet to determine the correct details for the ventilation slots on the top face.  Will update as and when available.

[G._Hoffman]

That rotated (compared to a Marshal) small piping Vox uses makes everything to do with covering the amp more difficult, but damn it does look stunning!  It's my favorite visual thing about my AC30, though I used white instead of the gold Vox uses.  I did finally figure out how to make the joints look good, though - make sure you have enough length to go around the amp completely (for my AC30, that would have been 3 yards), and cut it into three lengthwise sections - the wide center, the two narrow front and back.  The back intersects with the control cutout, so no joint is needed, and by doing the others separately, you don't have to make a joint across the piping channel, which is where all of my problems started!!!!


Gabriel

[DLPublic]

Gabriel,

I did finally figure out how to make the joints look good, though - make sure you have enough length to go around the amp completely (for my AC30, that would have been 3 yards), and cut it into three lengthwise sections - the wide center, the two narrow front and back.

Interesting idea.  Having never done this before, I was comtemplating wrappping the full width tolex around the box with the join(s?) at the bottom and then when set, cutting the tolex through the centre of the piping channels.  This, I thought, would allow me to push the gold string into the channel along with the cut ends of the tolex with it.  In your experience, would this work?

Looking at the image I found on the web below, it is hard to tell whether the tolex is cut flush with the edge of the channel or it overlaps into the channel. 

The back intersects with the control cutout, so no joint is needed, and by doing the others separately, you don't have to make a joint across the piping channel, which is where all of my problems started!!!!

I do not quite understand the bit about making a joint across the piping channel.  Can you please elaborate on what the problem is.

Thanks
Dave

[G._Hoffman]

Gabriel,

I did finally figure out how to make the joints look good, though - make sure you have enough length to go around the amp completely (for my AC30, that would have been 3 yards), and cut it into three lengthwise sections - the wide center, the two narrow front and back.

Interesting idea.  Having never done this before, I was comtemplating wrappping the full width tolex around the box with the join(s?) at the bottom and then when set, cutting the tolex through the centre of the piping channels.  This, I thought, would allow me to push the gold string into the channel along with the cut ends of the tolex with it.  In your experience, would this work?

Looking at the image I found on the web below, it is hard to tell whether the tolex is cut flush with the edge of the channel or it overlaps into the channel. 

The back intersects with the control cutout, so no joint is needed, and by doing the others separately, you don't have to make a joint across the piping channel, which is where all of my problems started!!!!

I do not quite understand the bit about making a joint across the piping channel.  Can you please elaborate on what the problem is.

Thanks
Dave

Where the two ends of the Tolex meet, you have a joint.  When that joint goes across the piping channel, it distorts, messes up the alignment of the joint.  This is one of the main ways I messed up the Tolex on mine, but by breaking the Tolex up into front, middle, and rear pieces, you don't have that problem, because each joint is only made for one flat section.  Take any advice I give on this with a grain of salt, though, as I'm pretty much a beginner at upholstery. 


Gabriel

[DLPublic]

Have made a start on the cabinet build using baltic birch plywood.  The main cabinet is cut from 18mm thick board, whilst the amp tray and the two back pieces are cut from 12mm thick board.

You can never have too many clamps.  Unfortunately I only have two sash clamps so I used my old picture framing clamp, which - you've guessed it - I made sometime ago.  FYI the item covered with polythene in the background of the second photo is a Farfisa Compact Duo organ I have owned since the late 60's/early 70's.  Needs a restoration job at some point - but that is for another time.

All the 18mm x 21mm pine battens are glued and screwed and the cabinet feels very sturdy.

The last two photos shows test fitting the amp chassis into the cabinet.  The chassis tray sits on strips of low density stiff foam to dampen vibrations.  I will add a close up in the following post.

As there is a four photo limit I will add some more in the next post.

Dave

[DLPublic]

The first three photos are the now sanded down cabinet.

I intended only inserting screws from the outside for the four front to back battens as is is difficult to get at screws from the inside.
However, I got a bit carried away and ended up also screwing the baffle support battens from the outside as well!!!  Just meant more sanding than necessary.

As promised the fourth image shows a closeup of the amp tray dampening system.

more to follow...

[DLPublic]

I have now received all the bits to complete the cabinet, i.e. tolex, grille cloth, corner protectors, handle, vents, tadpole piping and facia strip/gold string, etc.

Have just glued up a test piece (see last image) on which I will test out each stage first.

1) Rounding edges to fit the corner protectors.
2) Determining width/depth and routing slots for the gold string.
3) Determining width/depth and routing a slot for the baffle facia strip.
4) Practice fitting/glueing tolex, especially around corners (both internal and external corners).

I have decided not to install a scrim.  Instead the grill cloth will be held clear of the baffle by 4mm x 12mm d-profile moulding strips glued around the front edge of the baffle.  I have been able to set the baffle back into the cabinet by 3mm to allow for this.

Will keep you updated.

[sluckey]

Have you completed the amp chassis and tested it? How does it sound?

[DLPublic]

Sluckey,

Have you completed the amp chassis and tested it? How does it sound?

Have only tested open circuit voltages on PT secondaries (which also checked input fuse, neon lamp, mains switch operation) at the moment as am holding off ordering valves and speaker until early next month.  Hopefully the cabinet will be completed by then.

Dave

[tubeswell]

Do you have (or can you borrow) a plunge router with a 1/2" round over bit? (for the cab edges).

[DLPublic]

Tubeswell,

Do you have (or can you borrow) a plunge router with a 1/2" round over bit? (for the cab edges).

I have a Bosch router which I will use for the edges.  I gather the four side edges are 3/4" radius whilst the front, back and vertical edges are 3/8" radius to fit the corner protectors.  I have a 3/8" (i.e. 9.5mm) roundover bit and have just ordered the 1/2" one.

One reason why I will be trying it all out on the test piece first.

For the piping channels, I hope to use a small (1/8"/3mm?) straight bit with the plunge router attachment on my dremel.
Dave

[Willabe]

I gather the four side edges are 3/4" radius whilst the front, back and vertical edges are 3/8" radius to fit the corner protectors. 

One reason why I will be trying it all out on the test piece first.

Yes try it out on a test piece.

Fender used 3/8" on their cabs. I don't think 3/4" will work with 3/4" stock.

[G._Hoffman]

Do you have (or can you borrow) a plunge router with a 1/2" round over bit? (for the cab edges).

Doesn't need to plunge, just rout.

Tubeswell,

Do you have (or can you borrow) a plunge router with a 1/2" round over bit? (for the cab edges).

I have a Bosch router which I will use for the edges.  I gather the four side edges are 3/4" radius whilst the front, back and vertical edges are 3/8" radius to fit the corner protectors.  I have a 3/8" (i.e. 9.5mm) roundover bit and have just ordered the 1/2" one.

One reason why I will be trying it all out on the test piece first.

For the piping channels, I hope to use a small (1/8"/3mm?) straight bit with the plunge router attachment on my dremel.
Dave

Check the radius of the corners by holding them up to the corners.

You don't need to plunge for the string, as the channels run right off the edge.  Though, the best way I found to do it was with a 1/8" slot cutter with a bit extender.  Like so:



Kinda scary to use in a 1 3/4HP router, but it worked incredibly well.  I should have used the shaper.

I gather the four side edges are 3/4" radius whilst the front, back and vertical edges are 3/8" radius to fit the corner protectors. 

One reason why I will be trying it all out on the test piece first.

Yes try it out on a test piece.

Fender used 3/8" on their cabs. I don't think 3/4" will work with 3/4" stock.

It will, as long as you run the bearing on the face of the stock.  Best done on a router table or shaper, though, and not with a hand held router.  If you set it up right, it will go right to the opposite corner.  If you set it up wrong, you'll mess things up pretty badly. 

For the most part, 3/4" radius bits are pretty big for most routers, and I would much rather use them on a proper shaper.


Gabriel

[DLPublic]

OK the 3/4" radius round-over router bit arrived but it turned out to be 3/8" radius!!!  So will be looking for a refund.

So with that disappointment behind me, as there were only four edges (approx 10 inches long each), I decided to do the 3/4" rounded edges by hand using an electric plane and an orbital sander fitted with 40 grit paper.  The most important tool in this process was easy to fabricate from cardboard and that was the template.  The process used was as follows...

1. Draw lines 3/4" from each edge.
2. Using the template, draw the rounded edges on the end of each corner.
3. Using a plane, chamfer the edges, first at 45 degrees using 1mm steps to within about 3mm (1/8") of the line.
4. Again with the plane, chamfer the new edges of the previous chamfer at 22.5 degrees using 0.5mm steps.
5. Then with the orbital sander, sand down to top of line along the length of the edge.
6. Use the template to check along the edge and mark areas with pencil that require further sanding and keep checking/marking/sanding a little at a time until happy with the rounded profile along the whole edge.
7. Confirm corner protectors fit OK.  Et voilà.

Took less than two hours to complete as I took it very slowly, especially the planing stages.
The process is shown in the photos below followed by an image of the final result.

Next onto the other outside edges which will be rounded over using a 3/8" roundover bit on my router table and finally a 1/4" roundover on the top of the control panel cutout.  Will keep you posted.

Dave

[bnwitt]

Wow!  This project looks pretty darn good

[DLPublic]

Cabinet is now almost complete and ready for tolexing.  The baffle has three M4 t-nuts recessed approx 5mm along each edge for fixing from inside.  The upper ones have been filled as they will be covered with tolex.

I have glued a small frame to the front of the baffle for the grille cloth so it will be raised aproximately 3-4mm above baffle and a 3mm (1/8") wide channel (5mm deep) has been routed for the facia gold strip.  The valves and speaker (Celestion Alnico Blue  ) have now been ordered so have only drilled pilot holes for the speaker fixings until it arrives.  Intend to recess four bolts heads into the front of baffle (thereafter filled preventing movement) so speaker can be fitted from inside.

The gold string channels (3mm wide/deep) have also been routed around the cabinet and all the edges suitably rounded so that if needed I can fit the corner protectors later should the tolexed corners not be up to scratch.   The vent slots have been cut and t-nuts fitted inside for the handle and the four feet.

Next stage is cleaning the cabinet to remove all the dust from sanding, spraying the inside matt black including external corners, vent slots and finally fitting the vinyl, grille cloth, piping, etc.  I have ordered a litre tin of Evo Stik time bond contact adhesive for the tolex as this gives some time to work with it.

... to be continued...
Dave

[DLPublic]

Update 4 :~

Inside of cabinet was sprayed with matt black paint and the outside covered today with black basket weave tolex.
Baffle board now complete with speaker mounting bolts installed from front.  Quite pleased with the result.
I will give it a day or two before cutting along the two 1/8" channels to fit the gold string around the edges.

My corners are not perfect but still yet to decide whether to live with them or fit the plastic corner protectors.
Still need to tolex the two rear covers, but these should be relatively easy.  Then a final clean up of any left-over glue.

Need to cut some ventilation slots in the amp tray to provide air flow into the upper part of the amplifier which will expel through the two vents on the top.  The amp tray will also be sprayed black.

The 12" Celestion Blue and the valves have all arrived so should not be long before firing the Amp up.
Fingers crossed 
Dave

[sluckey]

Lookin' Voxy!

[DLPublic]

Finally got to fire up the AC15 amp.  Wow it is loud compared to my 15W Marshall MG15FX solid state amp!  The EF86 channel sounds sweet!  Just a few minor problems to sort out.  Testing and measurements (using a Draper DMM1A) were done with chassis on the table connected to the speaker which is now fixed into the cabinet. 

Both channels (ECC83 and EF86) work, however there is slight hum noticeable when each volume control is turned up past the quarter mark but does not seem to get any louder thereafter.  May need to re-visit the ground bus connection around the inputs.

Also past this point the EF86 channel start to produces a high pitched sound like some form of oscillation.  This can be alleviated somewhat with the high freq. cut off control.  Is this a symptom of microphonics?  How do I fix it?

Voltages are as follows:

V1 (EF86) - a     78.3V
                 g1    0V
                 g2    83.6V
           g3 & k    2.4V

ECC83s - V2 (PI)   V5 (CHII)  V6 (MOD)  V7 (OSC)
     a1       220V         146V        165V         96V
     g1         20V            0V       ~15mV      55mV
     k1         55V         1.13V      1.55V          2V

     a2       220V          223V       166V         212V
     g2         20V          3.1V      ~15mV      3.97V
     k2         55V        104.9V      1.55V       24.4V

EL84s -      V3         V4
     a        317V     315V
    g1           0V        0V
    g2       323V     322V
     k       12.2V    12.26V

EZ81 - k   345V
B+           322V  (i.e. voltage after the choke)

I need to order an ECC82 for the modulator (my mistake) which probably explains why the Vib/Trem does not work!

[EDIT: after sleeping on it and some research this morning, I now realise the Vib/Trem works when the foot switch is closed.  As I have not wired this up yet, this is probably the reason the Vib/Trem does not work.  Will try shorting the footswitch connection to test.  The ECC82 is similar to ECC83 but with less gain.  However, will still order one to match with the original design.]

Also there is quite a click/pop when switching the brilliance switch.

I need to investigate these issues further but not going to have much time over the coming week due to family commitments.

Dave

[sluckey]

the EF86 channel start to produces a high pitched sound like some form of oscillation.  This can be alleviated somewhat with the high freq. cut off control.  Is this a symptom of microphonics?  How do I fix it?

This tube is prone to microphonic ringing. There are silicon rings that can be placed on the tube to act as dampers. Using grommets to shock mount the socket may also help. Many times you just have to get another tube.

I now realise the Vib/Trem works when the foot switch is closed.

A simple fix that I used is a J12A switching jack. Just wire the switch terminal to the sleeve terminal. This will provide a ground to enable the oscillator when no footswitch is plugged in.

Also there is quite a click/pop when switching the brilliance switch.

Put a 5.1M resistor across the switch. 1M will probably work also.