YR,
You did change bias circuit to the revised one right? It's not just different parts values. It's now a half-wave rectifier circuit similar to most Fenders. (Actually a simpler circuit than before). The CT on the separate bias winding is no longer grounded. (not connected). Do you measure 58V across the windings as the schematic shows?
Geez Joe - that detail did slip my notice- will check it all through again - who feels like a knob-end?
Easy to miss, I should have labeled the CT "NC" when I did the revision.
Well - it's 4:05 am - it's quiet inside and out - and she breathes!!!! The old GT's are about 3mV adrift but all the voltages are RIGHT!!!
Thanks for everyone's patience - I really mean it - I know I'm a pain in the arse - tomorrow morning can't come soon enough!!! As soon as is reasonable it's sound test time!!!
I've now got a nice dance goin' on between the plates and cathode readings - so it's time to go and give the long-suffering Mrs. YR a cuddle - phew!!
Groovy, Rob. You solved the red-plating then? You're in control of the bias?
Did you make the changes JAM suggested?
This is great news! Another Hot Rod Amp reaching it's potential...
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Well - erm - not quite - I think I've shagged the OT - I've got a slot at John's workshop tomorrow afternoon between 3-5 to stick it on the bench and see what's what and have to phone Dave at Matamp after lunch to see if they've got any OT's that'd be of use - but JAM's revised bias is working great and I'm confident with a new and probably better OT it's gonna kick butt!!! I can get one made to order for about $60 from a local guy who winds 'em for Matamp. I'd love to just spring for a Merc or something sexy like that but I'm skint as usual... it'll give me an excuse to swap out those crappy TAD power tube sockets any road...
The reason I think the OT's knackered is because I'm getting very low readings from ground to the 2, 4 and 8 ohm taps - like around 1 ohm, wavering just above and just below - and I'm sure they should be more than that - don't know what made me check that but I suppose I'd gone through everything else - like - I noticed that I hadn't got both inputs going to both pins 2 & 7 on V1, I'd got the wire that should have gone to pin 6 on pin 7 of V2, and the wires going to pins 6 & 7 on the PI the wrong way round - all dumbass stuff because I was sweating and swearing my way through swapping those crap preamp tube sockets out into the wee hours of Sun morning... it's not quite as pretty as it was down near the tubes anymore but I'm real fussy about making sure the joints are sound - I hate doing work twice!!! But I'm sure none of that had anything to do with the OT giving up - I've revised my speaker outs now anyway and am going to put a switch in just to be safe... but thanks a million for all of this - geez - 4 pages!!! That's to everyone - and it's a good job it ain't a space shuttle, eh Fezz?
Got a OT from Dave at Matamp and will stuff it in tonight - fingers crossed!
edit - Have had to work through the weekend (the customer is always right) and upon getting said OT home and unwrapped it's got two separate primary and secondary coils - Dave works irregular hours but John knows a coupla guys at Dagnall who made this particular OT and will find out on Monday how to wire it - he reckons it's an 'interwoven' design - yet another fly in the ointment - but might be advantageous in terms of reducing heat in the coils... fingers are still crossed!
Last edited by yankeerob; 10-14-2007 at 12:55 PM.
Wooo - Hoooo!!!
She lives - she breathes - she sounds pretty amazing considering -
A. - I haven't been able to turn it up past 1 ('Do you have to do that now?' - erm - yes!!!) all the tone controls are at 12 o'clock and it is lusciously warm - both 'channels' are active so I can mix normal and bright to get a lot of subtle tone changes - I'm sure this will filth up a bit when I can turn it up but one things for sure - it sounds way better than when it was a HRDv and I haven't even opened her up yet...
B. - I've just stuck the original GT's that came with it in and biased it up - Fezz is spot with that 70% dissipation - it's at about 45mV/474V and sounds really happy... I can't wait to stick some decent power tubes in it!
C. - I've got three JJ ECC83s's in the preamp tubes - the Brimar/Mullards will make it really sing...
I can't believe it sounds this good - I though it was gonna be a bit grainy with those old tubes in (and I showed the schemo to Dave when I went for the OT and he said 'Oh, so you're building a Marshall then...' because he sees that tone stack and PI and doesn't think Fender - he's still a nice bloke though) but it's smooth, clean, full and not at all sterile - I can't imagine the tone it has, when turned up, will turn Marshall-like - every 50w Marshall I've ever owned started off sounding British and just got more so - this definitely doesn't. I can - at long last - confirm you can make a nice leather bag - might not be a silk purse - but a nice little leather bag - out of a sow's ear!!!
BTW - the OT was fine -here forgot that there's a lot of stuff bleeding off to earth when everything's turned right down - hence the very low DC resistance on the OT - thought I'd measure the DC resistance on the secondaries when I'd disconnected it but before I hoofed it out altogether - I mean - I didn't smell anything???...
- it would have been a disappointment to replace it as the whole point was to use the original iron...
When I get a chance to open her up I'll do some clips - I can't thank you guys enough - will publish the final schemo and layout no probs as I'm really confident this is gonna work for a while - it's very quiet as well - no real buzzes, hisses or farts though I was very careful to screen the inputs and the presence a la TJ's projects - the way the two 'channels' mix really kicks ass and you were right, Joe, about whether or not to bother with that S/R circuit - this thing sounds fine as is - I'd hate to spoil it - and won't - I'm gonna try it for the sake of knowing - good thing is it's easy enough to pull back out if it's crap - just goes in between the treble wiper and the 22nF cap - keep ya'll posted
Nice! The 5F6-a is a fantastic circuit isn't it? I was sitting about playing mine today and it's like being transported back to the late 50s.
They are also tremendously good Jazz amps. If you can, you should try something with a neck P90 through it, maybe roll off the guitar volume to half; talk about smoooooooth!
Glad it's all worked out for you.
Tommy.
Hey - no worries - yer - I know what you mean - I obviously haven't really gotten anything out of her yet but I use the neck pup on my Tele a lot - I have it raised just a little bit higher than what's generally recommended as I know the magnets are at about the right height to get really good punch but not too much string pull and it works fine and does get that nice jazzy tone when you roll the vol back...
Great job, Rob! I remember the first time I played my HRD-5E5A and had a similar reaction.
Just playing it low was wonderful; shimmery and crystal clear, warm and smooth with some tone setting changes...wondermous!
Of course, mine's not as friendly as the volume opens up since it's a 1-12 and not the 5F6, so I'm really anxious to hear yours.
I'm tellin' ya, these Hot Rod re-build projects are just too much fun. When the PCBs finally go, you've got a great set of hardware to work with.
Not quite the same as a tweed build in a pine cab, but sooo nice in their own right.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Tried the amp at volume before goin down the jam yesterday and am having probs with a horrible distortion that occurs when the amps just reaching natural saturation - we suspect there's not enough power in reserve so we're looking at beefing up the smoothing on it - I've also modded the schemo for any of you guru's to have a look at - depending on what tubes are in it there's between 474V/47mV (the GT's) and when I swapped 'em over for the TAD's it went to 491V/42mV for 70% dissipation - Fezz was right about doubting the TAD's although they were a used pair - don't know how they match 'em but there was about 8 mV difference between them - the original GT's only had about 2-3 mV difference - glad I've put individual 1 ohm'ers so I can see what's goin on - they do sound better than the GT's but - any road - we're looking at possibly beefing up the smoothing but here's a revised schemo that I'm gonna try in the meantime
http://images.lilypix.com/albums/use..._schematic.jpg
Rob,
I wouldnt put the choke after the screen grids. They like the regulation. You'll have less smoothing on the output stage where you've moved it. I had changed the two 47uf in series (2nd filter stage) on my Bassman to two 100uf like the first filter stage and got a tighter bass response. Do you have access to a scope? It would be helpful to know at what stage the distortion is occuring.
Thanks Joe, yer the guy who's looking at beefing it up for me has one - it's really weird - it sounds fine until it just starts getting into that sweet saturated distortion - when you strike a chord or a hard note it makes a horrible distorted BLATT and recovers - I was trying to avoid a trip to the bench but a tone generator and scope's gonna pinpoint where it's occuring - I'm really, really pleased with the tone - it's pure chicken, gravy and biscuits - just got work out the bugs...
So - I've gone back to this and then maybe up the value on those 47uF's?
http://images.lilypix.com/albums/use..._schematic.jpg
I'll post the schematic on the build I'm doing. It's basically the same as yours (based on the 5F6A).
So up until the amps starts to breakup - it sounds OK? Almost sounds like you could be describing blocking distortion.
http://www.aikenamps.com/BlockingDistortion.html
Thanks again for that link - it describes it very well and I'd say that is almost definitely what's happening - I'd definitely describe it as a transient distortion because it's fine when it's clean and at low volume but as I do tend to drive an amp hard I thought I'd better turn her up and see what'd happen under 'normal' circumstances - ie above 5... hit a few hard chords with the guitar full up and para 5 under 'Reasons' makes me think that's exactly what's happening.
Quick update - have tagged a couple 33uF's that I had lying around onto the existing 47uF's to get a little more smoothing there...
Have put a much bigger choke in...
And almost certainly found another problem in that the voltages on the anodes of the pre-amp tubes are fairly high - high two hundreds - working on dropping those - and have also found a stash of NOS Mullard 12AT7's (like hundreds...) so that'll be handy later on... first gotta drop these voltages... more specifics later - and BTW - since I couldn't get some new Winged C's quick enough I've gotten a pair of JJ's that have biased up quite happily but don't fit in the cage that's fitted to the HRDv - so that's gotta go 'til I can get some shorter tubes
Well the JJ's are in, settled down and biasing up very nicely - really stable - I've changed the 4K7 out on the positive rail of the PS for a 22K which has dropped all the voltages on the preamp tubes down to as near as what is specced in the original 5F6A schemo as I can get 'em with what I have to hand - 33K was too much - I suspect the next thing to try is a lower gain tube in V1 (a 12AY7 was the original spec?) - I have a TAD 12AT7 and a JAN GE 5751 to try - it's getting better all the time - still just starting to fart a little when I do some choppy chords a la 'Brown Sugar' (it should be noted that it was getting to a fairly uncomfortable v. level in my 16 x 10 living room) but it sustains very nicely and is VERY LOUD, bright & chimey if I want and although the bass has tightened up considerably since tagging some 33uF's onto the 47's in the second filter stage it still has plenty of bottom end if I want - it could be 'browner' but not bad at all for a FWBR. I just need it to be a reliable gigging machine and am probably pushing it to levels I'll never need in practical terms because it has - on about 4 - far more clean headroom and touch sensitivity than the Deville ever had.
Question for Joe - do you think it's possible that the bias is running out of gas and would upping the value of either of those caps help the situation? The range is spot on but I'm just wondering that when I'm getting to the 'tone zone' if you like - you know - just kicking over into distortion and this unwanted distortion occurs (nowhere near as bad anymore at all) - am I not making greater demands on the bias supply? I know it's all relative and interactive - it's bloody fantastic fun to try and figure out - but I do appreciate the fact you guys know more than me!!!
No, I dont think it would help. Try putting 1.5K resistors on the grids of the 6L6 (like BF Fenders) and see if that helps. You could also try lowering the value of the bias feeds from 220k to around 150K.Originally Posted by yankeerob
Question for Joe - do you think it's possible that the bias is running out of gas and would upping the value of either of those caps help the situation? The range is spot on but I'm just wondering that when I'm getting to the 'tone zone' if you like - you know - just kicking over into distortion and this unwanted distortion occurs (nowhere near as bad anymore at all) - am I not making greater demands on the bias supply? I know it's all relative and interactive - it's bloody fantastic fun to try and figure out - but I do appreciate the fact you guys know more than me!!!
Okey doke - thanks for that - I suspect - as I have just run the amp up again with that cheap 12AT7 in V1 - that that's gonna go a long way in taming the prob - can't fire it up at loud vol. right now but it's a lot quieter in terms of hiss when you turn the vols up - so that might just do it
Have you cleared up the blocking distortion?
I had some in my 5F6-A that I tracked down to a leaky cap.
You have hundreds of Mullard 12AT7s? They're great tubes.Are they MOD-surplus with white boxes and no Mullard logos (CV4024) or are they the later ones?
Tommy.
My source has described them as having MOD numbers so they might very well be the CV4024's - I already spoken to him about buying a quite a few off of him and he's cool with that - he wants to test them all so I'll get the cream of the crop - but yer he's convinced they are proper Bolton production valves...
Re blocking distortion - I've taken a number of measures - reduced the supply voltage to the preamp tubes which has made a huge difference and I've put a TAD 12AT7 in V1 which seems to have had an even greater effect - sound's deeper and cleaner - haven't had a chance to crank 'er up since changing the tube but I reckon it'll be OK. The JJ's aren't too bad though I prefer the voicing on the short bottles - will grab a pair of Winged C's now Watford are back off holiday or wherever it is they go when they disappear for a fortnight!
The code for the MOD ones is 5690-99-000-4024. Great tubes, enjoy!
Tommy.
I suspect one of these'd do the trick...
I took the beast down to the rehearsal room last night and discovered -
1. The preamp sounds great - not just good - but great - it's quiet and clear as a bell - the Tele sounds more like a Tele than it ever has - neck pup great toneful rhythm sounds - middle position - clear and deep - and everyone is right - you don't need reverb if you get it right and thanks to Leo, Fezz, Joe and TJ with a little thrown in here and there by others - it's perfect. Those M8162's are awesome bottles and even the used Brimars in V2 & V3 are doing the job magnificently!!
2. I still have a problem in the power section so I've come up with a new plan - the board I've made is a getting a bit ropey and though I probably could use it I'm making a whole new board for the power section with a new layout and schemo - not a lot different - just a bit beefed up as follows:
http://images.lilypix.com/albums/use...F6A_layout.jpg
http://images.lilypix.com/albums/use..._schematic.jpg
That should do the job and I'm buying all new caps apart from the 22uF's which are new anyway - it sounds amazing until it starts farting and we've run out of things it can be - I've ditched all the S/R stuff on this project - to be honest - although it's nice to have - I can only see it getting in the way of what's an absolutely crystal clean and deep sound - I just couldn't spoil that!! This amp is gonna be great for recording - I've never had something so loud be so quiet!!!
I suppose this'll be the final post on this one - I've got it running sweet - didn't bother with the new boards as per previous post - just swapped out the TAD 100uF's for Suntan ones from Rapid - swapped out the 47uF TAD's for 100uF Suntans in the 2nd filter stage as per Joe's suggestion - put a switch in to emulate jumpering the channels (I've gone with a 2 input layout instead of the standard 4 on 5F6A's) - removed the
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