gjm1553552756 Posted July 18, 2012 Posted July 18, 2012 Owen Young;168517 wrote: Dudes, We can use a process like this to learn how an amp works. Once we can figure out this schematic, then we can discuss/understand the merits of the design & tube amps in general. And in the process maybe ask/answer Qs about whether upgrading is of value. Japanese amps are well constructed, in a standard, good practice manner. (Aside from the Grounding, which is usually 'floating' - however, this NZ import should be Earthed.) I can help with that! Although it'll be October-ish before I have the necessary kit to do so... ;-) In all seriousness, I'm keen to learn how to do this.
Omegaspeedy Posted July 18, 2012 Author Posted July 18, 2012 Owen Young;168518 wrote: James, More Qs sorry: - A pic of the rear of the 2 PCBs - C7 & C1/C8?...do the twisted Grn & Or wires from C8 go to the 6SN7s? And do these twisted Grn/Grn & twisted Or/Or wires end up as 2 twisted Grn/Or prs? Thks. Hi Owen, I'll get the pics of the PCB's for you tonight. C8 green/green/orange/orange split into 2 sets of green/orange and one goes to BR2 and the other to the front blue LED power on light. I'll check which are the 6SN7 signal out wires and where they go. Cheers James.
Owen Y Posted July 18, 2012 Posted July 18, 2012 No hurry James, I'm a little puzzled about the HT (plate voltage) DC filtering - which commonly works by sending AC from the rectifier to a C-R-C or C-L(choke)-C combo called a Pi-Filter. Hence I wonder where is the R, or the L located in the chassis.
Omegaspeedy Posted July 18, 2012 Author Posted July 18, 2012 Hi Owen, I've pulled up the caps in the front end and have found that the C8 green and Orange DO connect to the sockets on one side, then tap off to the same position on the other socket and also tap off to the blue LED light. I couldn't see this under the caps. Apologies for the confusion. Here are some pics with the caps bent up and the three PCB's (do you need to know which one is which?) Cheers James Attached files
Owen Y Posted July 18, 2012 Posted July 18, 2012 That's excellent James, be gentle with those caps, 'massage' them back into place No problem, I should be able to identify the PCBs Note... you can appreciate now that the heater supply wiring is usually identifiable by the tight-twisted wiring. This is done to minimise/cancel hum radiation. Also, they are often conventionally coloured brown. Heater wiring is also heavy gauge because, even though it is low voltage (5v 300B, 6.3v 6SN7), the heating current is high (1.2Amps 300B, 0.6A 6SN7). Note also that heater supplies for tubes can be AC or DC... AC has more hum radiation/noise issues of course, but DC involves the complication of a DC rectification stage. With DHTs, AC is reckoned by some (incl me) to sound better. (More on DHTs vs IDHTs later, that's enough brain-bending for a day )
Omegaspeedy Posted July 18, 2012 Author Posted July 18, 2012 Great thanks Owen. It's all good stuff for the learning curve:) There seems to be a few instances where the left and right channel wiring is feed into one channel then the second channel is feed by that channel? i.e. the OTPs (Red wire) and the 6SN7 green/orange feeding one then across to the other. Is there an advantage in supplying both separately from the source i.e. one network of wires for each channel? You can hear this when you shut the amp down, one side runs out of juice before the other:) This must introduce a slight channel imbalance at a micro level? Cheers for all your help today.
Owen Y Posted July 18, 2012 Posted July 18, 2012 Hi Chaps, Yes ask the Qs, I will try to answer (if I can) & we can maybe we (me too) can learn a bit about how this gear really works... James, That's an interesting observation about one ch dying before the other... That could be due to either the heaters or the HT (hi voltage) shutting down. 1. Red HT wiring from C2-OPT-OPT: This is carrying 400+ volts DC from the last PSU cap C2, thru the primary winding of the OPT to the plate of the 300B. However, it is carrying only ~70mA & loops only a short distance betw OPTs. This 'tube current' is the standing current that 'biases' the 300B & exits via the cathode R of the 300B (the chunky gold anodised alumin cased Rs behind the 300B sockets) to Ground. This is a key cct loop. I would have thought that both ch's HT shut down would be unaffected by the extra few cms of wire...esp if you consider that the primary winding of the OPT would be a few hundred ohms 2. The Grn/Or wiring to the 6SN7s, is heater supply, carrying 6.3v/0.6A as mentioned. Yes it loops from one 6SN7 to the other & is usual practice. There my be some delay effect with the extra loop, but understand that the 6SN7 is an Indirectly Heated Triode (IDHT) & the heater coil is separate from the signal elements (plate/anode, cathode, grid) within the tube & heater current has little effect on the signal. (There is some capacitive coupling & possible hum transfer, but once warmed up, both tubes should operate identically.) There'd be greater concern about matching the tubes, I think. PS. Do you recall seeing any wires going through a hole/s in the chassis, into the red TX chamber, esp in the 'left-over' space above C2, next to the PTX? (I'm still wondering about that pi-filter choke or R.)
Owen Y Posted July 18, 2012 Posted July 18, 2012 Having said all that, you may have noticed theatthe 300Bs OTOH, have their 'filament' heating wires (Or) separated for ea ch. 300Bs differ because they are Directly Heated Triodes (DHTs), where the heating element & the signal carrying cathode element are one in the same! But more on that another time...
Owen Y Posted July 19, 2012 Posted July 19, 2012 Owen Young;168564 wrote: 2. The Grn/Or wiring to the 6SN7s, is heater supply, carrying 6.3v/0.6A as mentioned. Hmmm... there are 2 x 6SN7 heaters paralleled & therefore the combined portion of the heater wiring is carrying 2 x 0.6A = 1.2A. Which is similar to the 5v/1.2A filament load. However, the 6SN7 heater wiring used, looks much thinner gauge than the 300B filament supply :confused:
Omegaspeedy Posted July 19, 2012 Author Posted July 19, 2012 Cheers Owen for the technical explanation, I get the logic I think. If the signal isn't carried in that part of the chain, there isn't a signal to corrupt. Is this design DC or AC heated?
Owen Y Posted July 19, 2012 Posted July 19, 2012 omegaspeedy;168570 wrote: Is this design DC or AC heated? DC.... I think. To be honest, I still a bit puzzled by the connections to the cap PCBs. Here's sketch of the C7-C7 & C1-C8 bds, Fr & Rr. Sorry to be tedious but when you next get a chance to look inside, plse check whether there's nothing else connected to the front of these bds (apart from the caps themselves). I'm looking for some connection betw the +ve pins of these caps. Thks.
Omegaspeedy Posted July 19, 2012 Author Posted July 19, 2012 Not tedious at all Owen, I'll have a look for you. Cheers James.
Omegaspeedy Posted July 19, 2012 Author Posted July 19, 2012 Owen, I just looked at the pics on page 3 of this thread and it appears there are jumpers on the front (cap side) across the + terminals of C7/C7 and C1/C8. Take a look and I'll also confirm it when I take the bottom off.
Owen Y Posted July 19, 2012 Posted July 19, 2012 Yes they are jumpers joining the -ve(Gnd) terminals of the caps. I had noted that (sketch above). I was looking for any pi-filter/s arrangement, ie CRC or CLC, across the +ve terminals of the caps. If there's nothing else connected to the front of those bds (only the wires on the back) then...we'll move on. As soon as we confirm the schematic, then we can assess it. Thks PS. It would be good to know the values of all the caps, while you're at it!
Owen Y Posted July 21, 2012 Posted July 21, 2012 James, Another thing I can't quite pick up in the pics... the Grn wire from the Grid pin 3 of the 300Bs should feed from the 0.22 coupling caps (Mundorf), which in turn should connect from the Plate pin 2 of the driving 6SN7. There are also grid & plate Rs (the Grn ones I think) at ea of those 2 connections. Here's a sketch of my query...
Owen Y Posted July 21, 2012 Posted July 21, 2012 Here's the 300B & 6SN7 base diagrams for your interest: (Note: Bott view. The 6SN7 has a 'key' betw pins 1-8 which matches the keyhole in the socket.)
Omegaspeedy Posted July 21, 2012 Author Posted July 21, 2012 Hi Owen, I'll open her up in the morning and have a look. I'm borrowing SirAndy's Korsun KS99 amp at the moment because the Dayens Ampino is being borrowed by a friend for assessment in his system. My mate wants to purchase one for himself. Whats scary how good a US$300 Chinese integrated can sound! Certainly haven't felt like turning it off which isn't the case with the 300B. Lots of fun to be honest.
gjm1553552756 Posted July 21, 2012 Posted July 21, 2012 I too found it interesting how good some of the cheaper oriental kit can sound. A ~NZ$600 2A3 SE integrated set me on a slippery slope.
Owen Y Posted July 21, 2012 Posted July 21, 2012 James, So that you don't have to keep lifting the bonnet, I'll draw a wee diagram showing how & see the 6SN7 components, then you can dble check if correct. Stay posted...
Omegaspeedy Posted July 21, 2012 Author Posted July 21, 2012 No worries Owen, I'm not using this amp at the moment now so I'll leave the lid off. That Green wire connects to a 1Kohm resistor which splits off into two directions, one to the .22 Cap, the other half passes through another 220Kohm R then onto the bus bar closest the selectors knobs on the front panel. That bus bar then connects to a 470Kohm R onto Pin 4 of the 6SN7 socket. I've looked at the socket orientation and noticed the pins are all numbered as well. 4 it is. The amp is open Owen so feel free to ask any more q's Cheers James.
Owen Y Posted July 21, 2012 Posted July 21, 2012 Just a note about the 300Bs...you may have noted that the 2 filament pins are larger diam than the grid & plate/anode pins. Higher current & also partly so that your don't insert the 300B pins into wrong socket holes - the sockets have 2 larger holes for those pins. However, I have come across some modern sockets which are poorly designed/made, which allow the tube to be inserted wrongly, ie rotated 90/180deg! A trap that I've fallen into myself & can cause (electrical) damage.
Owen Y Posted July 21, 2012 Posted July 21, 2012 Hi James, This is an update of the layout showing the 6SN7 sockets, kindly check for me: - Some question marks over connections, eg R5/C6 (do I have this right?), R9/R10/C9 & r1a/R1b/blk wire heading north. - I have not shown the heater wire connections (H pins) for clarity. - Check also the vol pot ohms. You could note all the resistor ohm sizes & colour code bands - you may wish to familiarise yourself with the colour codes... http://www.michaels-electronics-lessons.com/resistor-color-code.html Generally all looks much as per the schematic mentioned early in this thread, with a few detail twists.
Omegaspeedy Posted July 21, 2012 Author Posted July 21, 2012 Yikes Owen, that's scary, that would cause smoke I'd think!
Owen Y Posted July 21, 2012 Posted July 21, 2012 Oh...re. the cap pcbs mentioned y'day... Plse note everything that is connected to +ve cap pins of the C7/C7 pcb & the C1/C8 pcb. (The + pins are on the top of the pcbs, the -ve cap pin is denoted by the wh stripe on the side of the caps.) The C5/C5 pcb is sussed I think - these are 300B cathode caps, which are connected to the gold finned cathode Rs of the 300B. Plse note the ohms of this R6. Note also the ohms of the VR2 'hum pots' - these are usually put in to adjust to balance out hum on the 300B filament/cathode. A Q about the PTX pin connections... Thks.
Omegaspeedy Posted July 21, 2012 Author Posted July 21, 2012 Hi Owen, Here we go, C9 bridges straight across the buses. No R10 for C9. Left C3 set-up. Pin K => C3 => R 470K => Pin G Right C3 set-up. Pin K => R 470K => R51 => Pin K Heres lots of close-ups. I check the rest, a bit mind boggling but I'm getting there. Attached files
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