I found a really good source for pots for my YBA-1 is Randall Aiken. His parts page is at: http://www.aikenamps.com/TechInfo.htm He's got all the correct values for a JTM45 conversion. Also, the pots he carries are the best quality around. I just replaced all the pots on my '66 YBA-1. Great stuff! Have fun! G. Sean Kilback wrote: At 11:58 AM 1/13/01 -0000, you wrote: From: rocca@adelphia.net Subject: tremble,middle and presence pots are these linear taper? I have to order a few and just want to make sure I'm getting the >right pots for my YBA-1. According to my schematic (I've noted the values I changed): volume 4M A (changed to 1M A) treble 250K L middle 25K L bass 1M A presence 25K L (changed to 5K L) A = audio taper L = linear taper happy swappin'! cheers, Sean --------------------------- hey Glen, I should have explained, sorry. Right after I sent the email I had that thought! :-) I changed the original YBA-1 presence layout to match the classic 5F6-A Bassman schematic. This meant removing R20 (4K7) completely and changing a couple of other connections as well. Check out the original and modded shematics on my page if you're interested. The Traynor presence configuration sounds ok but I prefer the response of the Fender design better. Seems to have nicer control over the highs, IMO. cheers, Sean From: Glen H. I noticed that you have changed from 25K to a 5K value on the presence control. What advantage(s) is there to this in terms of tone? Thanks in advance. Glen H. ---------------- No problem running triode mode as long as you provide seperate and larger screen resistors. I use 1.5K's and have not had a problem with them. If your going to make it switchable, us a good, wide body switch to avoid any arcing. On the EL84's you might get away with this if your using NOS 84's or 7089's ( might have that number wrong - the mil spec version), but I do think you would have do dump some screen voltage. You may have to go to a 2.2K to drop enough. I think it would be easier to drop the voltage on the center tap of the OT with a Zener than to get EL84's to work. Just my $.02 worth. Doug. I'm concerned about the EL-84 swap with the plate voltage that the YBA-1A (Mark II) uses. Is there an easier way to tame the plate voltage? I'm a novice. With a Bassmaster you can tie pins 4 and 9 together and run the tubes as triodes, but this isn't recommended for high plate voltages. Like I say, I'm a novice with just enough info to misinform someone. KO Aaron Turner wrote: > > I think pulling both of two valves might make it a bit too quiet, > but I am curious about a possible EL84 swap as I might be > able to get my hands on a couple of Mullard EL84s for nothing. > It would mean that it would definitely end up a guitar amp after > the modification though. Would it require any other changes? > Caps, resistors? > > Aaron Turner --------------- TAP It's definitely possible that you are right. Since Pete built Traynor amps to last, he may have built in a margin of error in things like current carrying capability of the trannies. Since it is near impossible to get data regarding specs on the old trannies (I have gone as far as contacting Hammond, and they have very little archive data), you have to guess and hold your breath. Therefore knowing, rather than thinking these were "over-spec" is impossible. I also agree that the earlier transformers were physically larger. However, that usually means that they were built to deliver more plate voltage. The heaters are run off a separate winding, and external size of the unit tells you little about the specs for that winding. One wild card thrown into the mix that can work to your advantage, is that Pete obviously bought transformers in bulk to get a price break. That means having fewer models, and using trannies with higher specs than required in certain amps, in order to simplify the parts buying process. One clear example of this is that the 2 x EL34 Bassmaster MKII and the 4 x EL34 Custom Special use the same Hammond Pt# A-1315 Power Transformer. As near as I can tell from this, it means that the PT in the Bassmaster MKII has a minimum of 100% current headroom in it's heater winding. In summary, there are some examples in the Traynor line where you can get away with what might otherwise be questionable tube swaps or additions. Knowing your stuff certainly helps - otherwise tread carefully. With Fenders and Marshalls, I would be much more careful. From my experience, both these amps were built with tight price points in mind. A mindset that there is zero tolerance for error will ensure you never get surprised. Craig --- In traynor-amps@egroups.com, "TAP"