rotaspec Posted July 20, 2010 Posted July 20, 2010 Also: It would probably be better to use one 6 amp diode and a 0.5 ohm 10 watt (or higher) resistor in series , but I haven't tested that combo. I have tested the three diodes in a quick lash-up and the heater glow is much more normal.
Shane Hanify Posted July 20, 2010 Posted July 20, 2010 Nice one Gary. It would be bad to see these little amps expire prematurely because of shoddy design if they can be fixed for a few dollars. Cheers, Shane.
rotaspec Posted July 21, 2010 Posted July 21, 2010 A couple of pics showing the diode string and connection to the PCB. There isn't actually much room under the transformer cover because it is made of 10mm MDF not plastic as first thought. Notice I used two 6A10 diodes in series with the 1N5408 removed from the PCB. That was because Dick Smith only had 2 diodes left in stock. I left long leads on the diodes because that is extra heatsinking for them. Any heavy silicon (non-Schottky) rectifier diodes will do. They get pretty hot so they must not touch the transformer or wires. I would have had more diodes in series but for the room and lack of ventilation. This lot only drops the heater voltage about 1v, but the valves look much less stressed and it ran fine all last night. The diode string is the better idea now that I think about it because the voltage drop remains the same no matter what the heaters draw. So if you put in some ECC88's the voltage won't rise as it would have with a resistor dropper. Attached files
Nak-Mad Posted July 22, 2010 Posted July 22, 2010 Thanks, Gary, Been following your work on this wee beastie with keen interest....keep it coming.... nice clear discussion for non-techo's like moi.. Tempting me more and more to have a go at tickling my one..... cheers Martin
Shane Hanify Posted July 22, 2010 Posted July 22, 2010 Thanks Gary, We have a bucketload of those diodes at work - use them in our boards. Given the height of the caps next to where the diode normally mounts could you not simply piggyback three of them? ] ] ] < like so, except vertically. now that I remember, we have piggyback stacks that are prefabbed for some cables. Would 4 be overkill? Cheers, Shane.
rotaspec Posted July 22, 2010 Posted July 22, 2010 Low Orbit;128208 wrote: Thanks Gary, We have a bucketload of those diodes at work - use them in our boards. Given the height of the caps next to where the diode normally mounts could you not simply piggyback three of them? ] ] ] < like so, except vertically. now that I remember, we have piggyback stacks that are prefabbed for some cables. Would 4 be overkill? Cheers, Shane. You could piggy back them but they would be in parallel not series, meaning the voltage drop wouldn't change. Also, then instead of one hot diode radiating onto the capacitor, you would have 3. I am wondering if mounting them on a terminal strip on the chassis just in front of the fan (if there is room) might be even better than having them up in the transformer cover. The reason is that I noticed that when the fan is running, there is air going into the transformer cover vent, which means that the hot air from my diodes is actually being drawn down into the chassis past the heatsink (exactly what I was trying to avoid). Having the diodes directly in front of the fan will mean their heat goes straight out through the fan. The downside will be that it will mean the fan will have to run all the time. The risk of overheating is when the amp is idle with the fan not running.
Shane Hanify Posted July 22, 2010 Posted July 22, 2010 Well, there's my duh moment for the day. Of course they'd be parallel. Yes, finding a way to (quietly) cool them would be good. Still, they shouldn't cause too much harm inside the transformer cover. Cheers, Shane.
rotaspec Posted July 25, 2010 Posted July 25, 2010 Well the diode string seems to be hanging together under the cover. I also got around to replacing the cheap and nasty source switch. I think it is actually quite a decent amp now, so it probably won't get cannabalised to make a preamp after all. I just bought an old Philips OTL valve amp (sans valves) that will make a great chassis for a preamp. Gary
Shane Hanify Posted July 25, 2010 Posted July 25, 2010 Nice one Gary, I'm liking mine a bit more with the new source switch too. I'm also assuming that 3 x 1N5408 chained will achieve the same result as in your amp? Cheers, Shane.
stephennic Posted September 8, 2010 Author Posted September 8, 2010 Hi everyone, Sorry to hear the news about Christchurch, I had my honeymoon there and other parts of the south island. Christchurch has been in the news quite a bit here in Aussie after the earthquake. Hope you all okay. Just a quick few questions, I was going to change the tubes in the valve hybrid amp. I was looking on the net for replacement valves to the 6N1 - seems a bit of confusion whether Ecc 88 is appropriate or ECC 40 or whether there is a proper equivalent?. If the ECC 88, is the elctro-harmonix 6922 or JJE88CC better?. For the 6P15 , which would you choose the Electro Harmonix EL84 or JJEL84?. Would you replace the the 6N1 or ECC88 valves or both? - are they all in the circuit?. One hifi shop told me not to worry about the valves - you must fix the heater circuit first as changing the valves wont make much difference etc. Will different valves make a difference. Any oppinions will help. Thanks Steve.
Owen Y Posted September 8, 2010 Posted September 8, 2010 Hi Steve, From what we have seen, this design is not your usual valve amp. Indeed it seems that some tubes are there only for 'looks', ie. they are not fully in-cct or contributing fully to the amplication. Until someone produces a cct diagram, I wouldn't be throwing $$ on tubes. It shouldn't be hard to draw a schematic if you have one of these amps & have the time. Maybe someone in Oz has done it?? With this in hand, you can then make sensible decisions on what may be worth investing some $$.
Owen Y Posted September 8, 2010 Posted September 8, 2010 Hi Steve, From what we have seen, this design is not your usual valve amp. Indeed it seems that some tubes are there only for 'looks', or only partially utilised. Until someone produces a cct diagram, I wouldn't be throwing $$ on tubes. It shouldn't be hard to draw a schematic if you have one of these amps & have the time. Maybe someone in Oz has done it?? With this in hand, you can then make sensible decisions on what may be worth investing some $$. That's my opinion anyway.
stephennic Posted September 9, 2010 Author Posted September 9, 2010 Hi, Thanks for the info. Got a quote today of $65 to do the heater mod. Will it change the sound of the unit at all if there are less volts running through the valves. Cheers Steve
Owen Y Posted September 9, 2010 Posted September 9, 2010 No, probably not, but they'll last longer & not glow as bright
SSEGRUB Posted September 9, 2010 Posted September 9, 2010 If you want to listen to some good Vintage ECC88 valves in it ,PM me when you are ready and I will post some out to you on to try on a no obligation trial basis. Cheers Paul
SSEGRUB Posted September 9, 2010 Posted September 9, 2010 If you want to listen to some good Vintage ECC88 valves in it ,PM me when you are ready and I will post some out to you on to try on a no obligation trial basis. Cheers Paul
stephennic Posted September 9, 2010 Author Posted September 9, 2010 Hi ssegrub, Thanks for the offer but I live in Australia, but I would love to try a few tubes. Has any one done the voltage mod - nakmad, rotaspec, owen etc. How did you go - improved the unit. Cheers Steve.
Nak-Mad Posted September 9, 2010 Posted September 9, 2010 stephennic;132646 wrote: Hi ssegrub, Thanks for the offer but I live in Australia, but I would love to try a few tubes. Has any one done the voltage mod - nakmad, rotaspec, owen etc. How did you go - improved the unit. Cheers Steve. Steve, No, totally guilty of total inactivity in that area .... beyond my meagre capability to DIY (shagging around with Nak transports is a doddle by comparison).. and real life, ongoing bathroom reno's, and a Nak 1000 refurb have taken priority. In fact haven't even turned it or much else on for best part of 6 weeks.. apart from a short burst to test out a resurrected Thorens TD520...
Shane Hanify Posted September 10, 2010 Posted September 10, 2010 Gidday Stephen, Rotaspec has had one of these to bits and stepped the valves down. The sound may have changed, but he attributes that to changing the opamp. It would be my instinct that changing the voltage of the valves would yield no change in sound at all, and changing the valves themselves only a small change. The greatest positive step would be the opamp, and the power supply. Cheers, Shane.
stephennic Posted September 10, 2010 Author Posted September 10, 2010 Hi, Well took the unit in to be done, get it back tomorrow. The guy said with the heater voltage dropped it maybe a little cleaner sounding with less hum thats about all. Let you know tomorrow. Maybe I should of asked him to do the op amps -mmm, I wonder how much that would cost - is it a large or costly job? Would any op amp do? Cheers Steve.
Graham D Posted September 10, 2010 Posted September 10, 2010 Are any of you guys interested in selling your Jaycar amp ? I think one of these would look so cool next to my modded 'vintage' Thorens turntable and my retro Grado headphones. Not sure if I would actually hook it up, just have it sitting there glowing in the dark ! Graham.
stephennic Posted September 11, 2010 Author Posted September 11, 2010 Hi all, Got the amp back late this afternoon after the mod. It sounded a little clearer with less hum through the unit. I took a risk and bought 2 new Sovtek EL84 replacing the 6p15 - $20 each tube. Put in in, after an half an hour it sounded smoother overall - lost a little of the brittleness at the top, bass a little tighter and punchier not as boomy, a little more spacial, maybe a little less warm sounding. Now Im wondering if I should replace the 6N1 - maybe a Electro harmonic 6922 or JJ E88CC. I keep you updated. Cheers, Steve.
stephennic Posted September 13, 2010 Author Posted September 13, 2010 Hi everyone, An update. I bought the electro harmonix 6922 Gold for a special price $20 each replacing the little valves. After an hour, dynamics have improved bass especially. The sound is more open and hearing more detail too. The voulme seems to have got louder too. I think the combined effect of the mod,replacing the valves have put the machine up another level. Some of the warmth has returned - I was initially worried when I changed the larger valves only, as it became a little colder sounding, but changing the little valves seems to make more difference - dynamics, openess, detail, which surprised me ( more than the big tubes -sovtek EL84), maybe its just the combined effect. It seems also less harsh when to on Rock music, I think the original chinese valves probably let the unit down a bit. I talked to the guy who did the mod, he made it about 6.3v, and put seperate caps on each channel. Another valve guy said before with the heater voltage so high it would of been like a car always running at 5-6000 revs, now it can just purr along. Nakmad its worth doing the mod and then change the tubes. I still think the unit and the tubes needs to break in again, its not as warm in the midrange but its not as mushy overall especially in the bass. If There was a negative at this stage- the mids are a little forward especially voices, and I say a touch less warm but just as musical with added clarity. They told me give the tubes and unit around a week to break in so overall - Im a happy chappy. Cheers Steve.
rotaspec Posted September 15, 2010 Posted September 15, 2010 Been off line for a little while as too busy. My unit is still running sweet, although I am not using it at the moment as I am experimenting with a few DIY designs. I did try ECC88 Mullards in mine, but found very little difference from the 6n1. However that was before the heater mod, and I didn't want to keep them in there suffering the high heater voltage. I still run the AWV 6CG7's in mine. I had thought of putting the EL84 in place of the 6P15, but dismissed trying it as I had heard horror stories from other forums when that was done in some amps. One of the pins is different between the two valves. I think it depends on which brand EL84 though. Gary
stephennic Posted September 16, 2010 Author Posted September 16, 2010 Hi Gary, One thing I noticed is the hum is nearly totally gone, and I have a lot more volume than before. Is that because the tube is a lot more sensitive or slightly incompatiable?. It sounds better than before even though its a touch more forward in the mids, its seems a lot more open and smoother and is less harsh on complex music too. The 6N1 is hard to find a direct equivalent on the net, but it does seem the 6922 are meant to be pretty close. The AWV 6cG7, are they the miniwatt tube, what country are they from? Cheers Steve.
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