Watkins Scout

[Daviedawg]

Over the period of lockdown I have bought and repaired a small number of modern amps. This week I managed to get a rare Watkins Scout. The Scout came just before the Dominator. I have not been able to find much information other than generalised statements and a couple of photos from eBay and Reverb.
With a bit of luck I will post some pics below of the condition as it arrived which was pretty good for a 1962/3 amp. It was totally silent according to the seller. A quick assessment told me that it is not exactly like a Dominator (and therefore 18 watt) circuit. Two obvious differences are the power valve cathodes have separate routes to ground. The second is that the trem circuit is similar but different. Otherwise it is recognisably like the 18 watt classic amp with some cap values different. It has a 16ohm 10" Elac alnico speaker which is in great order.
I powered up on the limiter after cleaning the valve sockets to be rewarded with a very quiet audio and a smoking first power supply resistor. After replacing the cap can I was able run it briefly. The EL84 cathode caps are also up the spout. But the quietness was because the preamp heaters had been rewired wrong. The two preamp valves are on a small independant pcb.
At the moment I am waiting for replacement caps. Meanwhile there are the usual things to see to like cleaning the pots, a new mains power cable and drawing up a circuit diagram.
One interesting point you will see in any pics I post. It is built on a tag board with hook shaped tags. The few pics I have seen and narrative on a vintage amps site (Hofner?) show a form of pcb with tracks on the top surface very like the Dominator pcb. I wonder why this one has the tag board despite being almost entirely original.
You will see that the HV is exposed on the two transformers when out of the cab. Care is needed when I am working on it live.
It came with a full set of old Mullards, all working satisfactorily. Once running I will do an audio demo.

Dd

[Bieworm]

Nice score Dd!!!

[crgfrench]

That is amp porn

[zaphod_phil]

Keep us posted, Dd

[Daviedawg]

Will do.

Dd

[Daviedawg]

The Scout is up and running after a wee wait for caps to come in the mail. It is possible there will still be some tweaks to come. So i will do some clips in a few days.
Interesting points about the Scout since there is not a lot on line about it. It has a three position mains voltage selector for 200v, 225v and 250v. I have it set at 225v as the nearest to the 235v incoming. This gives a B+ of 352 and EL84 plate voltage of 335v just a wee bit too high. So it may go in the 250v point.
The only piece of rework I found was wiring the heaters to the two preamps. And it was wrong serving only pins 4 and 5 which caused the silence the seller described. The cap can was all but a through circuit (good job I have a current limiter). The Mullard ECC83s are all in great shape.
It has a negative feedback circuit on the "normal" channel.
As found (and probably like this from build looking at the wiring) the third section of the cap can 20µF, was wired in effect to the same point as the second 40µF section. So there was hum. I saw this as I drew up the circuit so I rewired to a point after the PI power connection. No hum now. The PI and normal channel ECC83s have 56k plate resistors. The trem has 100k and then another 100k to the preamp only.
As well as the cap can all the caps (Hunts) on the board were toast. The black "plastic" cased ones breaking up and the white ones leaking. The flying ones to the pots are all ok. But I may still replace them. The cap can is a three section plus ground, 40/40/20. I fitted a 32/32 with a flying 22µF (to the correct spot) as a temp measure because it now looks untidy. So I need to get a three section can to replace it.
The circuit has similar make up to the Dominator Mk 1 but not the same. The power stage is as the Dominator with 0.05 coupling caps to the PI. The PI cathodes go to one 47k resistor and to ground direct. The normal channel is the same as the Dominator with some values adjusted. The trem channel is like the Custom 15 Dominator but not exactly the same.
The speaker is an Elac 10". It is in perfect order and sounds vintage. My Champ build sounds great through it.
I have photos but I just realised they are on my iPad. So they will follow sometime.
Both in circuit design and audio out this sounds like an 18 watt so the lineage is clear. It has been a super project helped by having few distractions and little else to do.
Be safe and no driving to your in-laws.

Dd

[Daviedawg]

Quick update. Took all the voltage readings at both 225v and 250c incoming. It is clear that the right setting is 250v. And playing it confirms that. Rounder sound with less stiffness. Familiar 18 watt tones.

Dd

[geoff 1965]

cool Dd! interesting project,are you going to draw up a schematic for future reference and comparison to the marshall 18W?
uncle doug did one with the early plexi and a fender bassman and it was clear to see what marshall did and very interesting seeing the comparisons.
looking forward to the pics and any clips,good work.

[Daviedawg]

The first draft schematic is in pencil. I need to go over it and add in some missing values. But then it should be ready to post. But I am too busy playing it to get back to staring into the board. But I can do it with just the back off as you will see from the pic above.

Dd

[fenderbass39uk]

As a Dominator owner and a general WEM enthusiast I am thoroughly enjoying your project. Thanks for sharing it with us. Regarding your comments about the tag board/PCB it could be a transition issue, they would never change over fully to a new way of working until old stocks were used up. Also I've noticed that Watkins were forever tinkering with details, slightly different circuit mods and component values etc.

[Daviedawg]

"Watkins were forever tinkering with details, slightly different circuit mods and component values etc."
You are correct there. There is a video on line by a gent Nick Adams I think, looking inside a Scout. I need to go back and look but I am sure I mentally noted differences from mine more than just the board. Constant improvement I guess.
You will know better but I have detected a serious brand loyalty for Watkins.

Dd

[fenderbass39uk]

Yes Nick Adams is very knowledgeable regarding WEM. He's sent me circuit diagrams and is always willing to share his knowledge- a true gentleman.
I think Watkins gear is a bit more flimsy and not as robust or as well made as Marshall. Great sounding though and it does have a certain charm.

[zaphod_phil]

Do you think there's a chance Nick Adams would be willing to share the Scout schematic with 18watt.com, since it was an ancestor of the Marshall 18W?

[colossal]

Very nice acquisition! Looks to be in fine condition.

[Daviedawg]

I've posted a couple of sample clips of the Scout in "Hear It" forum. Trem channel is brighter in both cases. The SF500 is good on this amp because it has a particularly sharp attack. The strat is on the middle pickup.

Dd

[fenderbass39uk]

Do you think there's a chance Nick Adams would be willing to share the Scout schematic with 18watt.com, since it was an ancestor of the Marshall 18W?

I'm sure he would if you contacted him via email.

[Daviedawg]

My schematic is drafted. I just need to draw it in a legible form. Today I hope. Minor differences from Nick's Scout but the same in the main parts of the circuit.

Dd

[Daviedawg]

Attached is the Scout schematic as I found it. The voltages are after replacement caps and some resistors of the same value. Using the 225v input ac selector gives values closer to those we target on the 18 watt. Nice simple way to see the effect of relatively small voltage adjustment.
There are some differences between this version which is early in the Scout production and later ones. It seems to have constantly evolved.

Dd

Scout schematic as found.jpg

[Daviedawg]

Just remembered I have not posted pics of the Scout as it is now. so....

Dd

Final internal shot.JPG

P1030036.JPG

P1030038.JPG

[zaphod_phil]

A beautiful vintage amp. BTW why is there a piston sitting on top of the amp?