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Lyndon Johnson 24th December 2016 02:35 PM

Upgrade ideas for 300B PP
I'm now the proud owner of an original 300 B PP and am very happy with how it sounds. True to form though I'm starting to think of what upgrades might be worthwhile. I would be keen to hear from anyone who has upgraded this amp, what they did and what the outcome was.


Greg. 27th December 2016 03:35 AM

Re: Upgrade ideas for 300B PP
Hi Lyndon,

Well, it looks like you have bought Gerry's amp so congratulations. Before you start any upgrade process, you need to know what Gerry or any previous owner has done. I'm not sure of your amps heritage but certainly Richard has previously been involved, possibly even the previous owner. If that is the case, undoubtedly I would expect some tweaks, or upgrades to have already been carried out. Furthermore, if it was previously Richards, it is also likely the previous owner to him was Neal Gibbons, a member here although ages since he contributed. He is also a tweaker so may have carried out some of his own modifications. I'm being highly speculative here based on my own little knowledge and I could be completely wrong. Maybe Gerry or Richard can confirm. My main message is, using the original schematic and build spec, check to see what has previously been done and exactly what it is you have. Is it altered or is it original?

I am happy to share with you my own 300B PP spec but please bear in mind that this is based on my own personal take on what can get the best out of this amp. Your preferences may be different so you may not be inclined towards all that I have done. The secret is to make one change at a time so you can assess the corresponding differences to sound you hear. Also be aware that I have never owned an original amp like you now have. I just loved it so much, at a much later date I built a clone albeit I used a very similar PCB and the chassis is of the original dimensions.

You will need to refer to the original schematic and parts list. Here we go........

C1,R3,R4 not fitted. Converted to battery bias using one per channel AAA NiCad battery (NiCad now hard to find. NiMH or alternative easier but they can bring a brittle edge to the sound whereas NiCad sound cool).

C2/5 to lowest esr Evox Rifa.
C3 (V1/V2 coupling) to VH Audio teflon V-Cap. When I did it it was pretty affordable. Will cost you an arm and a leg now.
C4 to Black Gate FK. Probably no longer available but gives you an idea what to go for.
C6/7 to Black Gate standard. Same availability situation applies.
C8/R10 and feed back loop omitted as of no value to me with the speakers I use. Likely to be the same for you.
C9/10 to low esr Evox Rifa.
C14-17 omitted owing to diode upgrade.
R1/5/6/8/15/16/17/18 to equivalent Kiwame.
R2 Vishay S102.
R9 to 12w non-inductive Mills.
R12/13 to 1K5 25W aluminium clad Please note that the value of this resistor depends on your intention on 300B plate dissipation. I have deliberately increased value to reduce dissipation to give my 300B's (plate life) an easier time (see more on this below).
D1-4 to 8A 1200v Fairchild FRED's. The reduced voltage drop and fast soft recovery these produce is the reason for omission of C14-17 snubber. However to further assist this voltage reduction and kindness to the 300B plates, I used Welwyn W22 120R voltage drop resistors immediately in line between L1/2 and C11/12.
Rectifier is Mullard GZ37.
I also introduced a DC heater circuit to feed V1/2. I am having some difficulty uploading this schematic to the thread so if you PM me your email address, I'll pass onto you the schematic and detailed instructions on how to implimemnt this additional circuit.

Valves have been the great and affordable Electro-Harmonix 300B gold grids coupled with some NOS options for V1/2. Your choice. I majored on Tung Sol and Jan Phillips.

Thereafter you can mess to your hearts content on the quality of input sockets, speaker output terminals etc. In terms of wire I used IPL Acoustic HU1 for hook up and their IC2 for signal wires.

Finally, I bypassed C2/5/9/10/11/12 appropriately. Again, if you need the minutiae, let me know and it can be detailed.

Hope that helps. It all depends on the type of sound you desire. I appreciate this is a complicated issue for discussion. If you would like to talk it over on the phone, just PM me your phone no. I'll respond.

For me, this worked very seriously. It took the original -300B to another level. In a sad kind of way, I have moved on from this amp and now use a commercial Devialet so my WAD 300B PP will be up for sale. Obviously, anyone interested, please give me a shout.


John Caswell 27th December 2016 01:33 PM

Re: Upgrade ideas for 300B PP
Hi Lyndon,
Why not run it for say 3-6 months to see what you think of it! Then maybe you can decide whether you want to,make it "better". I use this term advisably as no one has yet been able to define the term "better".
If you decide to upgrade then do it one item at a time, to decide what differences it has made, or not, and it may even be advantageous just to do one side/channel so you have a reference as to what it sounded like beforehand.
Whatever you do, do not attack it mob handed and change everything because someone else has done it, that is akin to putting your head in the oven and lighting it just 'cos granny said so.
I get many items in for repair because the customer read, "I have changed all the capacitors 'cos Joe Blogs said it is the thing to do" and then find it doesn't work because they either don't know what they are doing, - very common - or they are not watching what they are doing.


Lyndon Johnson 30th December 2016 09:48 AM

Re: Upgrade ideas for 300B PP
With all the festive goings-on it will take me a while to digest what you have both said but I can confirm:-
1) yes I will heed John's advice and not rush into things!
2) it is indeed Gerry's amp and the day I visited to buy it Richard called round. In between reminiscing obout 1970's kit speakers I did manage to learn that Gerry imported it from Canada about 10yrs ago and Richard got involved because it had a quite significant wiring error on one of the opt's , presumably from the original build. So he sorted that and tidied the wiring. It seems to be in original condition except the feedback switch on the back has been replaced by an earth post. So it is in fixed feedback- less mode. The only upgrade I am aware of is that the v1 - v2 coupling caps have been replaced by unbranded Russian(?) Teflon ones.

Chris 30th December 2016 01:23 PM

Re: Upgrade ideas for 300B PP
Hi Greg,

Any chance of some photos of your 300B amp, how does it compare with your Devialet amp, I do love the design of the Devialet but I also love the look of glowing tubes.


Greg. 30th December 2016 02:06 PM

Re: Upgrade ideas for 300B PP
Here you go.

Chris 30th December 2016 05:38 PM

Re: Upgrade ideas for 300B PP
Thanks Greg.

That really does look very good...:thumbsup:

Lyndon Johnson 4th January 2017 08:14 PM

Re: Upgrade ideas for 300B PP
Greg - that does look like a beautifully built amp. I am intrigued by your battery bias upgrade - presumably the batteries live outboard of the amp for charging purposes? You mentioned this first - is this because you rated it as the most significant upgrade?
I will PM you with my e- mail address because I am keen to learn the details of some of your circuit changes.
Incidentally, John raised an interesting question regarding "What is better?". What I am looking to improve is that rather hard to describe 'spaciousness' that valve amps bring. I guess it is all about reproducing those low level details in the music? The 300B improves on my 5881 in every respect except the afore mentioned spaciousness /soundstage /separation between instruments. Where I would say it is broadly comparable. The constraint could be the rest of my system of course, but it will be fun to try!

Greg. 5th January 2017 03:19 AM

Re: Upgrade ideas for 300B PP

Originally Posted by Lyndon Johnson (Post 86203)
Greg - that does look like a beautifully built amp. I am intrigued by your battery bias upgrade - presumably the batteries live outboard of the amp for charging purposes? You mentioned this first - is this because you rated it as the most significant upgrade?

No, I mentioned it first because it relates to components at the beginning of the component list. As I said, you will not be able to aquire now NiCad batteries, but you can experiment with others if you wish. Battery bias tends to bring the music more forward in presentation. The batteries are mounted inside the chassis, attached out of sight in my photo, to the inside of the front plate. You can just see a loop of red connecting wire I used. They are generally fit and forget because they receive a charge when the amp is running. I did change mine after over five years use, however the ones I removed were still holding charge and working fine. You could also try resistor only bias. You will loose some gain but the sound will be slightly different.

I have sent you an email.

John Caswell 6th January 2017 03:20 PM

Re: Upgrade ideas for 300B PP
Hi Lyndon,
I have use battery bias in my PhonoIIi/III for years now and find it excellent! You may still be able to buy "tagged" NiCad" batteries, they don't have to be large either "AAA" or "AA" will do, if you cannot get them then "C' cells will be fine just larger. Do not be tempted to buy the standard cells and fit them in holders - I have found since the de leading (Pb) of a lot of things contacts tend to corrode much quicker and noisy contacts result.


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