It would be interesting to know the difference in screen current with 4k7's versus 2k2 resistors. Have you tried tying the raw bias voltage to the suppressor grid on the smaller Traynors with EL34's as is done on Custom Specials? And for unrelated info -------------GE 6550A Max plate voltage 660V Max plate current 42W which is the same current rating as a KT88. Max screen voltage 440V Max screen current 6W (10W peak) Peak current rating is higher than max rating for a KT88 Svetlana 6550C Max plate voltage 680V Max plate current 35W Max screen volts 400V Max screen current 6W MO valve and Svetlana and possibly Tesla/JJ KT88 Max plate volts 800V Max plate current 42W Max screen volts 600V Max screen current 8W Interesting info for those swapping to 6550's for high voltage Traynors The GE's have the potential to be biased a little hotter or possibly to produce more power, but considering the price of GE's (if still readily available) I would go for the Russian or Slovak KT88's Regards: Reid ------------------------------ With the new crop of higher quality tubes, it seems that the prospect of having a meltdown due to the ~540VDC on the plates of your YBA-1A is lessened, compared to using some of the cheesy '80's tubes. Upping your screen resistance has a direct effect on overall long-term reliability, though. I mount all of my screen resistors directly on the sockets (between pins 4 & 6) and increase them to a minimum of 1K 5W. This position change has no implication to performance, as near as I can tell. If you decide to use a single 2K2 (or other value) 10W resistor mounted on the circuit board, you should stand it off by allowing longer lead lengths. I don't know how many Traynors I have seen that had the single screen resistor, lying flat to the board, with obvious "toasting" marks of the board underneath the resistor. If you drive your amp hard the resistor will get hot. My experiment with the 2K2 value is recent, and I like the results. I noticed in a recent post to Ampage that Kevin O'Connor advocated using higher screen resistance in amps primarily used for distorted tones in order to get a more "singing" quality. This is in keeping with my own observations. Since this is fairly simple surgery, I am going to try various values in excess of 2K2, and decide on the one or two I like the most. Craig ---------------------------------- I use 7.5 watt cements mounted on the tubes sockets and change the feed resistor to a 1K - 3K 7.5 watt resistor (I like around 2K the best, but it does very a little with the amps voltages). The 5 watt parts typically don't have the voltage rating high enough to be safe. The other cool side effect of using two resistors, is that it is very easy to install a pentode/triode switch. You can't do that with a common resistor. Besides, if they hadn't meant for you to mount the screen resistor there, why would there be an extra, unused lug on the tube socket? Regards, Doug A person can never have too many guitars or fishing rods. Have Fun & Be Happy! dwoodall@iname.com http://www.familiarstrangers.com -------------------------- From: To: Sent: Monday, April 23, 2001 11:28 AM Subject: [traynor-amps] Re: 6550's and KT88's - Caution actual Traynor content. Thanks.....with the heat absorbed from these things, is it OK/prudent to use 15 watt resistors, especially if I just replace the one resistor, or is there an unintended bad effect from increasing the wattage of the resistors? I mount all of my screen resistors directly on the sockets (between pins 4 & 6) and increase them to a minimum of 1K 5W. This position change has no implication to performance, as near as I can tell. if you decide to use a single 2K2 (or other value) 10W resistor mounted on the circuit board, you should stand it off by allowing longer lead lengths. I don't know how many Traynors I have seen that had the single screen resistor, lying flat to the board, with obvious "toasting" marks of the board underneath the resistor. If you drive your amp hard the resistor will get hot. Doug BTW, I have started running 2K2 screen resistors in all my higher voltage Traynors. If anything, I think it improves the responsiveness and feel of the amps. I have been thinking about trying out 4K7's, just to see how they work. I've never tried to figure out how much that drops the voltage that the screens see, though. Craig --- In traynor-amps@y..., "Doug Woodall" wrote: You have to know what the plate voltage, then determine the proper bias current for a given plate dissipation. Given the rather large plate dissipation of the KT-88, I would start around 60% and see how it sounds as well as what's getting hot. I probably wouldn't go over 75% PA for the KT88. However, I don't think the 6550 are going to survive long in the high voltage MkII as their Vg is only about 450V (off the top of my head). At the very least you'll need to install 1.5K screen resistors (should do that anyway). Other than the screen resistors, I don't think there is a issue with installing these tubes in any Traynor I've seen. Doug Woodall http://www.familiarstrangers.com ------------------------- Hey Tony, Found these with a Yahoo search. Hope it helps. http://www.caseman.com.au/clothsamples.html http://www.timeelect.com/Ampparts.htm P.S. You might as well give up looking for the original knobs. I have some info on some pretty silver ones to match that silver grille cloth though. ;-) Jim ----------------- The Traynor silver grille cloth can be purchased through a number of Canadian music stores. I'm talking to Murch Music in Cambridge, Ontario and 12th Fret, In Toronto Ontario. As for the knobs, check out Songbird Music in Toronto. They provided me with a some Traynor knows a couple of years ago. All three of the stores that I have mentioned have web sites and their real nice people to deal with. Rick Hi Bruce, The surge diodes are there to absorb large transient voltages across the primary of the output transformer, such as when operating the amp with no load(!). They're there to protect the transformer in other words, so leave 'em alone unless they've gone bad (shorted). I did remove them from my '68 Custom Special because they looked pretty ratty. Instead I installed 1N4007 diode strings to ground, as is done in some Ampeg amps. This mod is also shown in the Pittman tube amp book,it does the same thing as the surge diodes in the Traynor. Check the schematic for your amp, it should tell you what load impedance your amp wants to see. Mine is 8 ohms, however it has no problem driving a 4 ohm load.Driven into heavy clipping by an alterna- punk bass player,in my son's band, the transformers don't even get warm. Four ohms would be better than 16,tube amps cope with a lower impedance much better than a higer one.It's definitely a good idea to install a 3 wire cord. Some people like to remove the ground switch and capacitor at the same time. This allows you to use the hole the ground switch was in for some other function. The capacitor in your picture looks original...30 or so years old! Your tech will probably want to replace all the electrolytic capacitors in the amp, which is a good idea. Some techs, myself included, also like to install individual 1000 ohm, 5 or 10 watt screen resistors for each output tube instead of the "shared" 20 watt screen resistor originally installed. Its a great amp, enjoy yours! Dave --------------------- On a side note, the Sovtek 5881WXT can take the higher plate voltages and is a very reliable tube (that's why you see them in many of the mass produced amps out there). It may cost you some power due to the way it's made (I've been told it's really neither a 6L6GC or true 5881 but a military tube that the russians came up with for reliablility situations). I didn't say you would like the tone though, that's in the ear of the listener. A friend of mine loves them in his SF Twin even better than Philips 7581A's. As far as 6L6 types go, it's hard to beat the Philips 7581A for clean headroom and able to take the voltage. I've had good luck with them in my Ampeg B-15 running about 515Vdc on the plates. tap ------------------------ > So how do the OEI & the Victoria compare??? They both sound better than the Hammonds. Clearer mids, clearer and punchier bottom end, sweeter highs, and much, much chimier. The differences between the two boiled down to the fact that the OEI is for EL34s and the Victoria is for 6L6s. I won't play them with my band for a while, because we are in the process of mixing 11 songs (with 100% tube Traynor guitar and bass tracks!!!), but I can't wait to get to try these heads live. The amp that the Victoria tranny went into wasn't my own. It belongs to a buddy of mine. I was so happy with the OEI and so sad that I couldn't keep the Victoria that I will soon order a Victoria OT for one of my own amps. The amp with the Victoria OT also had a Weber Copper-Cap rectifier installed. It is a little metal box which imitates the sag of a 5AR4 tube rectifier with power resistors, diodes, and other circuitry. Technically, the head should now sound very much like a tweed bassman. Does it? It's as close as it can be. I don't think that there exists a better 50W Plexi OT than the OEI and likewise I don't think that there exists a better tweed Bassman OT than the Victoria. That was the reason why we chose to purchase those two. They are expensive, but worth every penny. I'd rather have one or two totally killer amps than a collection of good amps. BTW, does anybody want to make a trade with me? I have an old Signature, no tube rectifier, in great shape and I want a 60's Bassmaster with choke also in good shape. My e-mail is different from above. It is gabasa@sympatico.ca Thanks to Tim at Song Bird for doing a good, clean job as usual. Gord