Blue Note

Hello Myles, It's been a while since I've needed to bother you but I ran across a review on Harmony Central about a modification done to a Marshall JCM 800 model 2210 amp that I would like your oppinion. The post said " I snipped C3 and rewired the Ohm selector switch switching the 8, 16 ohm positions" he claimed this made his clean channel "as clean as a Super Reverb" and really "smoothed out" his distortion on the hi gain channel. These are what I have always felt this amp needed except I would like to smooth out the hi gain and also sweeten up both hi gain and clean channel. If you could describe what it is he may have done and whether or not you would recommend such a change, or if you have another remedy for these results I sure would appreciate it. I tried to email the guy who made the post but no response. Thanks for Your time, Blue Note

Myles, Its been a while since I was on the net but noticed your thread kind of getting pushed back in the pages. I have just gotten so much good information from you on this thread that I don't want a new member to miss the oppurtunity to "Feel Free to ask Myles" so I thought I would give you a bump. Later, Bluenote

Myles, I was looking through a Guitar magazine last night and noticed a full page add on Electro Harmonix tubes. According to them they have better than NOS 12AX-7's, 6V6's designed for 475 plate volts, 6L6's designed after the RCA black plates and EL-34's that sound like Mullards. I was just wondering if you have had time to test these and if you share the same opinion. Thanks, Blue Note

Myles, Thanks for the advice on the 2120, I placed my order for some 12AX7C's from Groove Tubes and I am anxious to try them out. Thanks again. Blue Note

Myles, I have won a bid on ebay for a digitech 2120 processor. My guess is you don't care for these and I am not a big fan of these complicated programmable devices either but hey they quit making them and I guess the collector side of me said that since it is obsolete I gotta have one. Any way it has two 12AX7 tubes in it and before I even attempt to start tweaking on the sounds I would like to replace the tubes. Do you have a recomendation? Thank You, Blue Note

Myles, Just wanted to thank you for answering my question back on page 44 about the dependability of a silver face Champ. Sorry it took so long for me to get back to you. Later, Blue Note

Hello Myles, It's been a while since I have had a question worthy of your expertise but I have been enjoying reading yours and others posts, now for the question. Is a silver face Champ dependable enough to play a 3 hour show three nights a week. The place where we are the house band for a music theatre dinner show type deal has such a good monitor system that I can hear myself fine plus cut down on stage volume by using the Champ. I put a new WeberVST speaker in it about a month ago and really like the sound I'm getting going through a Boss GT-6 then to the Champ but I have been a little concerned about the dependability of the amp plus how long can I expect the single 6V6 to last in a class "A" type circuit which I think is the class a Champ is in. Thank You, Blue Note

Myles, I recieved my GT bias tool kit and MHG-SAG kit last week and finally got around to working on my JCM 800. The two matched sets of STR-450's from Mesa Boogie were within 10% of each other but I chose to put the matched quartet of Svetlana's from Mike at KCA in and set the milli-amp draw at 36. The amp sounds better than it ever has. Thanks for all your help. Blue Note

Myles, I got some of the Siemens STR 450's on the way from Mesa-Boogie for my JCM 800 dual channel with reverb model 2210, the tech service guy said even though they are not sold as matched quads (only duets) that if I ordered them all at the same time they would be matched, sounds kind of questionable but I'll give it a try. About the B+ voltage do I need to measure this with the new STR 450's or could I measure that with the tubes I currently have. They said it would be about a week and a half before I got them. When I order the SAG-MHG kit from GT is it important to get two new tubes for the reverb circuit, if so what do you recommend. I am planning on ordering the bias tool also with my order from GT, I know there are other bias tools available is this the one you would buy? Thanks again for Your help!!! Blue Note

Myles, Thanks again for your help, I am trying to locate the tubes you suggested but no luck as of yet. As far as the B+ voltage I'm not real sure where to measure this, is their a certain pin# on the tube socket that would give me this and is this in reference to ground. Also as far as dialing in with milli-amps do I put my meter in series with the bias circuit for each tube? if so can I just unsolder the wire from the tube socket and place meter between wire and socket. I don't have one of the milliamp bias probes but will get one if just placing a meter in series will not work. Thanks again and I plan on contacting you also at GT about the SAG-MHG kit. I am really enjoying the tube report I think it's great you are willing to share what had to take a lot of time and effort with everyone. Later, Blue Note

Myles, I finally am getting around to retubing my Marshall, it is a dual channel with reverb JCM 800 model 2210. I would like your preferences on both the pre-amp and power tubes. This amp came from Marshall with 6550's which I had converted to EL-34's back in 1991 at a amp shop in New Jersey. Even though the amp tech disagreed I insisted on using Groove Tube pre-amp GT-12AX7's and GT El-34 power tubes and also using only two power tubes instead of four to lower the overdrive volume of the power tubes. The only new tubes I have is some sovtek EL-34WXT's that I bought about six years ago and the guy sold them to me then at a discount because he said they had them forever. I don't know exactly how old they are but the box they are in is turning yellow and even though I don't have it with me right now I think they both had a sticker on the box with 370 wrote on it so I assume they are a somewhat matched pair. I know this is not a lot of info but do you think these tubes are any good. Also I noticed the "GT-12AX7" is not available any more I think its only GT-12AX7R, or GT-12AX7C. The GT-12AX7's really have not been played a whole lot and thought these may still be better than any new ones available today. But then again these tubes may have not been tested to be a matched Driver tube. The reason I think the amp needs retubed is evidently the amp tech in New Jersey had the amp very much under biased because the GT label paint is burned to the point it has even flaked off and I think this means they have been running to hot. Also I think I remember you suggesting to get a true Marshall sound the amp needs to have just a hint of crossover notch still on the scope. Do I remember correctly? Thank's again for your help and expertise, Blue Note.

Myles, Thanks for the info on the 12AX7 inverter, I haven't had a chance to work on the Princeton yet but since I don't need a matched 12AX7 I have every thing I need and hope to get a chance this week. Just thought of a question over the weekend, in between sets I have always turned my standby switch to off, but the other guitar player in the band always leaves his on. We normaly take a 20-30 minute break and I was wondering if maybe I was causing more harm than good by doing this. Also how much time before the gig should you turn your amp on to let the tubes warm up. Just want to make my amp and tubes last as long as possible. Thanks for your time.

Myles, I got a couple more questions. I started looking at my Princeton Reverb last night and noticed the phase inverter was a 12AX7 instead of a 12AT7. I then went to schematic and it says the phase inverter is only using half of the 12AX7. So my question, is a matched phase inverter important in this design? And if so would a 12AT7 be alright? I have some matched AT7's but no AX7's. Also I asked a couple of questions about my Champ, the sine wave and some Sylvania tubes in a earlier post. I know you have many questions to answer and probably just missed it. Hope I'm not driving you crazy with so many questions. The good thing is just a couple more amps then I'll have to buy some more to work on. Which will probably take a while. Thanks again for your help.

Milobender, No I do not mind you are anybody else jumping in on any thing I have posted. I will let Myles tell you what you should use because I am very new at this stuff and except for a few electronics courses in college really don't know much about electronics. I just love tube amps and have several that I could afford to collect over the years. I wish money was not a problem so I could buy more but I just can't stand to think the few that I do have are not sounding the best they could is the reason I started messing with this stuff. I have two 8 ohm 100 watt resistors that I use with my scope. I plug one of the resistors into the speaker jack for a 8 ohm load or paralell the two if I need a 4 ohm then hook my scope right across the resistor. This may not be right so I'm glad you asked the question Myles may say this is wrong and you'll be helping us both out. Later.

Myles, I spent a little more time on my Champ last night. I figured out what I was doing wrong with my scope. I had not readjusted my voltage level on my scope from my last amp which had a lot greater power output. I am able to see the whole wave now but for some reason the bottem half is distorting a lot quicker than the top. This is the reason I thought I was only seing half the signal when I got it turned up enough to make a signal the bottom was already flattened out. Is this normal, it sounds fine playing with a guitar through a speaker but I have never noticed such a difference in my other class AB amps. I also found some more old 6V6's lying around and after going through the whole pile again I deciced to go with a Slyvania with black plates. Don't know how old the tube is or even where it came from, do you remember any Sylvania 6V6's with black plates, and if so what do you think of them. Thanks again