Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 1blueheron on August 19, 2021, 11:12:05 am
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Just acquired a Traynor YBA-4.
I don't have it in my hands yet but looking forward to picking it up next week and seeing what I have.
I already know the power cord needs replaced (lots of electrical tape) from pictures.
Looking at the schematic, it appears is has a death cap and a polarity/ground switch. Planning to remove the death cap after new 3 prong is installed if it hasn't been already. Prepared to replace electrolytics if need be.
Grill cloth needs replaced. If anyone has a source for grill cloth that matches closely, please let me know.
Anything else to be on the lookout for and any suggestions?
From what I have heard about these, they sound great but are a little on the loud side :l2: The 15" speaker is supposedly the sonic achilles heel of the amp if it has one. I would like to get it and play with it first and hear for myself, but if I end up swapping speakers in this combo, any tried and true suggestions?
Another thing I am wondering about, is the viabilty of swapping out the 6CA7's with 6V6GT for less power. Schematic shows plate voltage as 433V. I know 6V6 can survive at this in some amps but I am ignorant on the effects of bias and what impact this would have on the OT.
Thoughts on best ways to attenuate appreciated.
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More pics
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The 15" speaker is supposedly the sonic achilles heel of the amp if it has one. I would like to get it and play with it first and hear for myself, but if I end up swapping speakers in this combo, any tried and true suggestions?
I have a WGS 15" alnico speaker that I love, pricey though.
I think Sluckey has a 15" Weber that he likes a lot?
Another thing I am wondering about, is the viabilty of swapping out the 6CA7's with 6V6GT for less power. Schematic shows plate voltage as 433V. I know 6V6 can survive at this in some amps but I am ignorant on the effects of bias and what impact this would have on the OT.
Taking out the 6CA7's and putting in 6V6's will decrease the load on the PT, less current draw with the 6V6's than the 6AC7's, so the B+ dcv will rise.
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You realize this is a ***BASS*** amp, right?
I have an Eminence Big Ben 15" speaker in my Marshall 18 watt amp. :laugh:
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You realize this is a ***BASS*** amp, right?
No. :laugh:
I told you I'm not reading things, seeing things right, says right on the schemo title 'Bassmaster".
I don't see anything in the schemo that looks like it's designed for bass, looks like normal guitar amp coupling cap values? No K bypass caps at all. Has a Hi pass T filter between V2a and V2b. Channel 2 has a bright cap across the vol.
Probably sound very good with a guitar plugged into channel 2. Might need to add some small K bypass caps for a little more preamp gain, and maybe take out the T filter, but maybe not? Maybe up the B+ filter caps for nodes A and B? Might even decrease node D to a 10uF or 8uF.
https://el34world.com/charts/Schematics/files/Traynor/Traynor_bassmaster_yba4.pdf (https://el34world.com/charts/Schematics/files/Traynor/Traynor_bassmaster_yba4.pdf)
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You realize this is a ***BASS*** amp, right?
I have an Eminence Big Ben 15" speaker in my Marshall 18 watt amp. :laugh:
Yes, I realize it is supposed to be a "BASS" amp. I suspect it will be used more as a poor man's Marshall JTM 45 than doing Bass duty, although we could use a good bass amp too.
If that Big Ben sounds OK in a Marshall 18, it would probably sound good in this beast as well?
My understanding is that Pete basically copied and tweeked the old Fender Bassman 5F6A circuit for this amp? Easily modded to a "Marshall" ?
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traynor bassmaster (heads and combos) are basically a poor man's plexi
yes remove death cap, yes change electrolytics (i do this as a matter of course on old amps). i would not try 6v6s in here (i usually change the bias feed resistors to 150k and throw in 6550s, especially the 90w yba-1a that is probably fine with the xf2 mullard 6ca7 but i would suspect they eat up current production tubes)
some of these had adjustable fixed bias. if it does not, make it adjustable fixed bias and throw some 1ohm 1% resistors between cathode and ground so that you can measure and set bias better than the rather cold stock setting
some of these have some odd long tail pair resistor values (one had 47k grid resistors?). i change these for more marshall values (1M)
some of these have a big ole cement resistor across the output jack to protect the output transformer if somebody forgets to plug in a load. i remove as this can rob some power
i repurpose the polarity switch to add a cathode bypass capacitor to one of the preamp stages
these are great amps and, at least the heads, were constructed in a way that servicing them only required removing the top panel (not having to disassemble and remove the chassis is nice!)
don't forget to jump the channels like you would to an old four hole marshall
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If that Big Ben sounds OK in a Marshall 18, it would probably sound good in this beast as well?
My reason for choosing the Big Ben was because I built my 18 watter in an Ampeg cab that required a 15" speaker. Big Ben was the only British voiced 15" I could find. I was pleasantly surprised because it makes my 18 watter sound big like the 50W Marshalls.
My understanding is that Pete basically copied and tweeked the old Fender Bassman 5F6A circuit for this amp? Easily modded to a "Marshall" ?
Yes, just rip out all the stuff between the plate of V2A and grid of V2B. Convert V2B to a cathode follower and tweak some TS caps, and you have a JMP 1987 Plexi. Oh yeah, minor tweaks to V1 components too. I'd want to hear it just as is for a while though before converting. Just might be a keeper as is.
I always wanted one of those old Traynors but just never ran across a good deal.
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I'd want to hear it just as is for a while though before converting. Just might be a keeper as is.
Yep. :icon_biggrin:
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in my opinion these sound good mostly as is, no need to do a full plexi conversion
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Thanks to all for positive words and encouraging feedback on this aquisition. Makes me even more eager to get this fired up.
All of the YBA-4 schematics I can find are badly photocopied and hand drawn. Looks like the mimeograph leaked a bit or something. Hard to make out some of the values. My eys are getting to old to decipher chicken scratch.
I have done my best to copy and clean it up for posterity but there are a few values I remain uncertain of which I have left in read. If anyone can validate, that would be great.
Sounds like there may be several different versions and revisions floating about. Wondering which this will be and how true it remains or if it was already plexified or possibly otherwise butchered. I see from the pic someone put Groove Tubes in it which I am sure were not Pete Traynors OEM.
Traynor amps have always had an emotional tie for me. My dad had a Traynor YVM-3 amp and a pair of Traynor tower speakers when I was a kid for a PA system he used when performing instrumental concerts. I had sound man duties frequently. I also used to hook my stereo up to it an shake the house when my folks were not home. I have a lot of family from the Batavia NY area. I think my dad bought that amp at the Batavia store. It would have been between 1973 and 1975. It went away after my dad passed. When I saw this amp for sale, seeing that logo the trim, and the the strap handle brought back a lot of memories. Hoping this amp will do the same for my son as he plays with it.
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if the combo is like the heads, there likely is a schematic stapled to the cabinet (the heads one has to remove a few bolts and the top comes right off to service. GREAT design)
i would wait until this gets to you to figure out what revision you may or may not have
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You see red. I see blue. :icon_biggrin:
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^^^awesome^^^! Thanks Sluckey.
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I picked up the beast yesterday. I am very pleased so far. This was truly a barn find type deal. Straw , dust, dirt, spider eggs, cocoons, etc. But underneath that dirty tolex and haze of dust and dirt was a very unmolested Traynor YBA-4. Speaker is dated June 1976. Everything except for the output tubes appears to be completely intact and original. Phillips/Mullard 12AX7A's are all there. Does not look like it has ever been opened or worked on. The tolex cleaned up pretty good. It has one small tear on the side that I think can be glued back down pretty easy and will barely be noticeable. Taped up three prong power cord is original. Apparently at some point in the 70's Traynor actually began using the 3 prong cords and the schematic under the lid shows this. I will be updating schematic accordingly. The board is a little bit warped which I understand is normal. Has all the original mustard caps.
So, the big question. Does it work? Yes. I had a scare at first. Plugged into the top jack of channel 1 and had nothing. Tubes lit but not a hint of anything out of the speaker. Was heartbroken and figured either speaker was shot or OT was fried. Removed the speaker and ohmed it out at a perfect 8 Ohm's. Cleaned it up, put it back together and turned it back on and tried one more time, this time in the lower jack of channel 1. To my surprise, it worked. :think1: I am not terribly familiar with the 4 jack setup on this amp but apparently if only one thing is plugged in an no jumpers installed, it must be in the lower jack. Will review schematic more closely to see if this is correct and logical. Same thing on channel 2.
How does it sound. LOUWWDDDD. Too loud for use in the house, at least with the present pots which at this time seem like the only thing in need of attention or possible replacement. I did not notice any significant hum, or any in sizzle, crackle smoke smell, or heat of the Electrolytic caps. They seem to be fine, at least for now. I am thinking I will probably just go ahead and replace the pots. Existing pots are plastic knurled shaft and very scratchy, loose feeling and not smooth at all. Very touchy. Volume setting 2 is louder than comfortable and 3 requires it be moved outside as dishes begin to rattle and lightbulbs shake and the dog hides under the bed.
It was after 10 last night when we got home, got it cleaned up and plugged in the first guitar. Didn't have time to play with it too much without waking up the nearest neighbors 1/2 mile down the road. Will likely be keeping them up a bit tonight. Plan is to take it out on the porch and let it stretch its legs a little bit and play with jumpering it. We did try it with both bass and 2 string. Both sound very good although the 6 string does have a bit of a boost in the upper mids which is a little bit overbearing and can cause some pain to the auditory nerve. :l2: No doubt this thing is going to be some fun but I am thinking of investing in a good attenuator. would like some suggestions for taming this beast for less than stadium size venues.
Here's some pictures I snapped last night.
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more
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Schematic stapled inside cabinet top.
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Looks good. :icon_biggrin:
Speakers front loaded.
I'd try cleaning those pots before changing them. And clean the input jacks while your at it.
Those filter caps look original, pretty old, I'd change them all.
Both sound very good although the 6 string does have a bit of a boost in the upper mids which is a little bit overbearing and can cause some pain to the auditory nerve.
It is a bass amp, so it might be the speaker? Try a couple of different different speakers, don't have to be a 15" to test it.
It might be the T filter between V2a and V2b. That T filter is a big part of that preamps voicing, (along with no K bypass caps) with those caps and resistors. I'd just temporarily disconnect it at it's in/out and jumper it to hear how it sounds without it. You could always hook it back up then.
The TS slope R could be made a little larger, it's 47K, try 56K. But I wouldn't do that until I changed all the lectro filter caps 1st.
And lastly, I'd try gator clipping in some K bypass caps, to hear how that sounds.
All these things will depend on if you want a bass amp or guitar amp. A little harder to try and make both sound great.
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apparently if only one thing is plugged in an no jumpers installed, it must be in the lower jack. Will review schematic more closely to see if this is correct and logical. Same thing on channel 2.
That's not correct according to the schematic. The jacks are wired exactly the same as the Fender Hi/Lo jacks. You should get sound from any of the four jacks. Try cleaning the offending jacks.
PS... I lightened up your schematic to make it easier on the eyes...
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Also Traynor amp used a single series screen grid R, most install 1 470ohm/3w screen grid R for each power tube. You can leave the shared screen grid R in place that's already there or take it out.
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tonite's activity plan...
1. Clean input jacks
2. Attempt to clean pots
3. connect extension cab for guitar and listen.
4. Replace grill cloth if I can find a close replacement cloth on the way home.
I will report back on test results. Want to get a good baseline before I make and changes or mods.
Appreciate the feedback from you guys. Very helpful. Thanks for making the schematic easier on the eyes Sluckey!
Willabe, what effect does the shared vs individual resister have on sonic fingerprint? Speaking of that, I have no idea if the EL34's were properly biased when they replaced the original 6CA7's.
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.... what effect does the shared vs individual resister have on sonic fingerprint?
It's not for sound, it's for better G2 (screen) protection. Some stereo audio amps used to use a single shared G2. I've read that's where Traynor got the idea from. :dontknow:
And modern tubes don't seem to be able to handle the stress that NOS tubes can. After all the screen grid is just a thin wire that can over heat. The screen was always a weak link in pentode power tubes in guitar amps because they pushed them soooo hard.
As far as sonicly, if you increase the value of the G2 R, it will start giving more compression as you increase it's value. You will also start to loose some volume. But many amps are too loud anyway. :think1:
Some/a few guys recommend nothing smaller that 1K for modern 6V6/6L6, EL34, etc.
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no idea if the EL34's were properly biased
Add a 1 ohm resistor to each cathode of the EL34's instead of them going straight to ground, then you'll have an easy test point for bias
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I like classic Traynor amps, and have a few.
Personally, I like the two of them that are bass amps stock, when using them for guitar (with one exception - see below). You can take that with a grain of salt if you like. I am not generally the type to say "how can I make this non-Marshall amp sound more like a Marshall" or "how can I make this non-Fender amp sound more like a Fender". I buy amps like Traynors because I want something different from a Marshall or a Fender, but still awesome in ways that I like. So my preferences not to mod, or mod too much, right away, might be different from yours. But again, I like Traynor bass amps pretty much stock, for guitar use.
The one I have that is closest to your YBA-4 is a YBA-1 Mark II. In addition to being a head only, there are a few other differences, but overall they're close.
A few thoughts about this comment:
Both sound very good although the 6 string does have a bit of a boost in the upper mids which is a little bit overbearing and can cause some pain to the auditory nerve.
You may already be aware of this, but maybe not, so I'll mention it. If you plug into the "bright" channel - that's the side with a 0.001uf cap strapped across the volume pot - you will obviously get a high-end boost.
In my opinion, the bright channel can be a bit much. I actually think that most of the time - the stock / standard treble bleed cap is generally a bit much for my taste, on most amps (not just my Traynors).
You've got options, before going crazy with mods.
One thing I have found can work well on my YBA-1 is the widely-used jumper-the-channel-inputs approach, as shown on this four-input Marshall pic I just googled-up in case you are not familiar:
https://www.tdpri.com/data/attachments/166/166154-6f551abafe3d61b3327276a4fd6e1a6f.jpg
I like to do this anyway when going for hard-rock guitar tones on my YBA-1, because you get more gain. But it also lets you blend in more of the non-bright channel (turn it up higher), and less of the bright channel (keep it lower). So yes, this gets you more drive and gain - but it also lets you mix the two channels together in ways that affect the overall tone.
Another option is to replace the volume pot with one that has a switch on it, to switch the bright cap in and out according to preference. I have done that. It works. Some people try a smaller value bright cap. Others just cut the bright cap right off, which is a fine approach if your bright cap hatred is pure enough.
And yes - these are loud amps. I like them that way. There are many options for trying to limit the decibels coming out of an amp that was designed to be loud. Some work reasonably well, others do not; most have significant pros and cons. I'm not sure there is an easy, perfect solution, but plenty of things to try.
I think one that is too often overlooked, is to find a different speaker with appropriate power handling (wattage), but lower SPL. I preach about this too much I guess, but there really is a noticeable difference in the volume put out by a guitar speaker rated at 97 SPL vs. 101 SPL. I don't know how many 15-inch, 100-watt-plus, 97 SPL (or lower?) guitar speakers are out there. Maybe? Or if you are OK switching to another cabinet, maybe try a 12" of sufficient wattage but lower SPL.
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no idea if the EL34's were properly biased
Add a 1 ohm resistor to each cathode of the EL34's instead of them going straight to ground, then you'll have an easy test point for bias
in my experience these are generally biased pretty cold to begin with. that's why i like adding a trimpot in there along with the 1ohm 1% current sense resistors
one thing to note with the 1 ohm resistors is that you'll have to do a bit of rewiring of the sockets because pins 1 and 8 are all wired on one chain to ground. may save some troubles figuring out why the darn thing worked before you added em ;-)
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I'd probably install the 1Ω resistors like this in that amp...
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Replaced the power cord and cleaned the input jacks last night. Didn't get into cleaning pots yet.
No luck on the grill fabric yesterday. Found something I think will work today.
Was too late to test the input jacks when I finished up last night.
Tested it out this AM and all jacks worked great. Bass sounded good in the bass input and guitar sounds good in the guitar inputs. Just as my son was channeling his best David Gilmour tones out of it, it suddenly went silent and the pilot light went dark. I quickly flipped the power switch off and pulled the top. I have one of the large filter capacitors that was just slightly warm. Smelled like I might have a bad cap somewhere. I also remembered while driving to work that the amp has a breaker which I did not check. Didn't have time to troubleshoot further.
This has me a little worried. Hopefully I can find the problem and resurrect it tonight. My primary suspect right now is a rectifier diode. I vaguely remember the filaments still on power tubes glowing as I reached for the power switch. If breaker tripped they would have gone dark. I will plan to get some new caps for it just to be safe. It was sounding pretty sweet before lights out though. I'm a little bit bummed right now though. :sad2:
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.... My primary suspect right now is a rectifier diode. .... I will plan to get some new caps for it just to be safe.
Those diodes look original, modern diodes are better now. For safety I'd change all of them, including the -bias diode. (I like ultra fast diodes/ UF, easy to get now a days. Less switching noise.)
Agree to be safe change all the electrolytic caps, including the -bias lytic caps. Look carefully at the -bias R's for cracks, heat discoloration and test them for resistance.
If the bias goes down, diode or filter cap, big trouble. :w2:
That amp uses 'mustard' caps for the coupling caps, highly prized by many. Try to keep those if you can. :icon_biggrin:
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the one i had with the circuit breaker (they didn't all come with em) the circuit breaker was faulty so i replaced with a normal fuse holder
but yes i'm the kinda fellow who would've replaced the electro caps before even firing up, as they tend not to like sitting unused for years/decades
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I have one of the large filter capacitors that was just slightly warm.
That's not good. Filter caps usually operate at ambient room temperature. You know what to do.
Those diodes are high quality and rugged. Probably last forever unless another component such as a shorted filter cap takes them out.
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I quickly flipped the power switch off and pulled the top. I have one of the large filter capacitors that was just slightly warm. Smelled like I might have a bad cap somewhere.
FWIW;
Caps can and do explode, EVEN with power off, so it's good to leave sleeping dogs lay til everyone reaches ambient temp. A face full of cap guts is not fun
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the one i had with the circuit breaker (they didn't all come with em) the circuit breaker was faulty so i replaced with a normal fuse holder
but yes i'm the kinda fellow who would've replaced the electro caps before even firing up, as they tend not to like sitting unused for years/decades
Guess I will find out tonite what the penalty is for not replacing caps first.... :sad2: That's not a bad idea on the fuse holder vs. breaker if neccessary. Possible the heat got to it when I soldered in the new cord.
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I ordered the 40uf/450v and the 8uf/250V filter caps last night. I don't see much out there in the way of choices for the 60uf/63V. Looks like 47uf, 50uf, and 100uf are the standard values now available. I would assume in this role more is better rather than less, so I ordered a 100uf. If this is wrong headed, please let me know.
Last night I pulled the tubes, plugged it back in, hit the popout breaker, and turned it on. The pilot light lit and I have 6.8V between filament leads so it looks like the PT is still alive. I didn't want to leave it on long to check much more until I get those caps replaced.
Looked for cracked resistors and burned spots or evidence of arcing or shorts that may have caused the breaker to trip but don't see any evidence of that so I will assume the capacitor shorted as it heated up and blew the fuse as a result.
I came up with a home brew grill cloth solution which I did as a team project with my son last night.
Here is the before and after. ( or after and before as it posted. Lol.)
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While you are waiting on caps check the resistance of those two cap cans (4 caps in all). Check from positive terminals to chassis.
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I ordered the 40uf/450v and the 8uf/250V filter caps last night. I don't see much out there in the way of choices for the 60uf/63V.
You need 500v caps. That schematic says 440dcv and that dcv will be higher at turn. Wall acv is higher now so it could be more than 440dcv now. F&T makes 500v caps.
The 60uf/63v for -bias? Doug sells a 100uf/100v that would be fine.
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While you are waiting on caps check the resistance of those two cap cans (4 caps in all). Check from positive terminals to chassis.
OK, Checking resistance of caps + to ground I read infinite resistance on 2K setting. This is with the caps at ambient temp.
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I ordered the 40uf/450v and the 8uf/250V filter caps last night. I don't see much out there in the way of choices for the 60uf/63V.
You need 500v caps. That schematic says 440dcv and that dcv will be higher at turn. Wall acv is higher now so it could be more than 440dcv now. F&T makes 500v caps.
The 60uf/63v for -bias? Doug sells a 100uf/100v that would be fine.
Good point, I was just thinking stock values would be sufficient.
I can get 500V and 600V 105C caps in 40uf. 500V still isn't much of a safety margin if I am upgrading. Would it be wasted money to bump up to the 600V?
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I can get 500V and 600V 105C caps in 40uf. 500V still isn't much of a safety margin if I am upgrading. Would it be wasted money to bump up to the 600V?
Yes may be a waste to buy 600v caps. The 500dcv caps will be fine if the amp stays under 500dcv at start up. And they can take another 25dcv or so for several seconds while the power tubes warm up and start drawing current.
Hi- temp is good.
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Replaced the electrolytics in the bias circuit today and got it prepped for the PS filter caps. The 500V caps should arrive tomorrow with any luck. Also removed the "death cap".
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Update,
Forgot Mon. was labor day and no mail service. Had to wait til yesterday to get the power filter caps but they did come.
Good news..
The new caps are now soldered in. Since the original can brackets wouldn't work on the new, smaller caps, I made some new brackets and mounted them on a couple peices of scrap circuit board. Still deciding if I like this solution.... It seemed like the best way to preserve original wiring. Easy to convert back. I kept the old caps and brackets. Thinking of other options that might work and be a little neater as well as provide better access to pots than my current solution.
Bad news....
After getting the caps all in, I noticed the getter on one of the two EL34's is turning. Looks like I am going to have to break out some more money.
Since I am now forced to buy a tube, I am considering going back to 6CA7 vs the EL34's. I guess none of what is labelled 6CA7 today is a true 6CA7, It looks like the two most affordable candidates are the Electro Harmonics or the JJ. Alternatively, I have some spare 6L6 I could throw at it. Any opinions on the EH vs JJ or going with the 6L6 appreciated.
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i have used conduit clamps from the hardware store to secure electro caps before. usually helps to bring the caps with you so that you get the appropriate size. i have also drilled holes to add a can cap or two (had em sitting around in the right value so why not?)
i don't think it makes much of a difference whether you use el34 or 6ca7
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Ordered some big bottle JJ 6CA7's last night.
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The new JJ 6CA7's came in today.
If time allows, plan to install the 1ohm resistors as suggested tommorrow and will check and post actual voltages at all the pins before installing the new tubes. Don't want these to go poof.
This is the first SS rectified amp I have worked on. I am used to being able to pull rectifier tube and check PT voltages. Any special procedures for checking a SS rectified amp?
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I would leave the PA tubes out til you verify -bias voltage AT the socket
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Just put the amp in standby mode to check PT voltages. Do as shooter suggests too.
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I fear I have done something wrong? :dontknow:
I installed the 1ohm 1% resistors between pins 1&8 and attached pin 1 on both to common chassis grd.
Next, with all tubes removed, I powered on but left in stdby.
I showed -39.5V on pin 5 of V4 and V5
Next, with all tubes still removed, I checked voltages at each pin.
V4 & 5
Pin 1 469v 0 (grnd)
Pin 2 3.4v
Pin 3 471v
Pin 4 471v
Pin 5 39.5V
Pin 6
Pin 7 3.4V
V3
pin 1 465v
pin 2 0v
Pin 3 0v
Pin 4&5 3.4v
pin 6 466v
pin 7 0v
v2
pin 1 464v
pin 2 0v
pin 3 0v
pin 4&5 3.4v
pin6 462v
pin 7 0v
pin 8 0v
pin 9 3.4v
v1
pin 1 464v
pin 2 0
pin3 0
4 3.4v
5 3.4v
pin 6 464V
pin 7 0v
pin 8 0v (grnd)
pin 9 3.4v
Why is everything showing up as 460-470V? Can't think straight tonight. Maybe doing something wrong.... will try again tomorrow night.
Here is a pic of the installed 1ohm 1% resistors. Don't have any good bias trim pots on hand will see about getting some.
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Why is everything showing up as 460-470V?
Because you pulled all the tubes.
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I installed the 1ohm 1% resistors between pins 1&8 and attached pin 1 on both to common chassis grd.
Next, with all tubes removed, I powered on but left in stdby.
I showed -39.5V on pin 5 of V4 and V5. Next, with all tubes still removed, I checked voltages at each pin.
V4 & 5
Pin 1 469v
Pin 2 3.4v
Pin 3 471v
Pin 4 471v
Pin 5 39.5V
Pin 6
Pin 7 3.4V
Pin 1 can't be 469v, that's the suppressor grid, grid 3, and you grounded it.
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Thanks guys for the sanity check.
So, I was confused on my pin 1 V4,5. It is indeed grounded and voltage is 0
So, if I am interpreting correctly, I should expect voltages to run high because there are no tubes installed to pull them down to operational level. Is that correct?
Would you check anything else before installing tubes and taking another set of voltage readings with tubes in place?
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Use a light bulb current limiter with a 60W to 100W incandescent bulb. If the bulb does not glow brightly, then plug the amp straight into the wall. Check voltages on V4 and V5, pins 3, 4, 5, and 8. Pin 8 should be approx 30mV to 50mV.
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Last night got the light bulb limiter assembled and it lit very dimly.
Plugged it in directly tonite and took readings. Here is the result with line voltage of 121V.
V5
Pin 3 = 461
Pin 4 = 456
Pin 5 = 39.8
Pin 8 = 31mV
V4
Pin 3 = 457
Pin 4 = 453
Pin 5 = 39.8
Pin 8 = 31mV
V3
Pin 1 = 217
Pin 2 = 39
Pin 3,8 = 41
Pin 6 = 255
Pin 7 = 38
V2
Pin 1 = 117
Pin 2 = 27
Pin 3 = 28
Pin 6 = 184
Pin 7 = 0
V1
Pin 1 = 209
Pin 2 = 0
Pin 3 = 1
Pin 6 =218
Pin 7 = 0
Pin 8 = 1
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Plan to check resistors tonight for drift and see how they look.
Would like to go ahead and play with installing the additional screen resistors as suggested. Is this the correct/best way to add them?
The amp sounds much better with the new 6CA7 tubes.
There is a slight "rushing of wind" type noise when the amp is turned on. Not a hum, more like white noise. Any ideas on the cause?
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Would like to go ahead and play with installing the additional screen resistors as suggested. Is this the correct/best way to add them?
Yes, that's fine like that. But keep the lead on pin 4 short, it is a grid stop R. Grid stop R's work better/best with a short lead.
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Would like to go ahead and play with installing the additional screen resistors as suggested. Is this the correct/best way to add them?
Yes, that's fine like that. But keep the lead on pin 4 short, it is a grid stop R. Grid stop R's work better/best with a short lead.
To keep the R lead shorter, maybe I should solder one end to pin 4 and terminate the other end directly on the tube socket chassis screw beside it.
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To keep the R lead shorter, maybe I should solder one end to pin 4 and terminate the other end directly on the tube socket chassis screw beside it.
What????
Your talking about the screen grid R correct? That has dcv on both ends.
Just solder the R to pin 4 1st. Keep the lead ~1/4". Then run the R over the top of the socket, you run that R going to pin 6 up in the air a little, on an angle, so it's lead will be a little longer.
Just looked at your drawing again, it's wrong. Pin 6 does not get grounded. Pin 6 gets the feed for the screen grid dcv.
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It appears I was confused between screen resistor and a grid stopper. :think1:
I think I now understand. Screen resistors should go between pin 4 and B+2. I would just be using pin 6 as a junction point for B2 feed. You are saying to keep the resistor lead between Pin 4 and the body of the resistor as short as possible. I will move the B+ lead that is presently tied to V5 Pin 4 from the existing 470R 10W, to Pin 6 of v5 and then to pin 6 of V4. Resistors go up and over from pin 4 to pin 6. Is this all correct?
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You are saying to keep the resistor lead between Pin 4 and the body of the resistor as short as possible.
That's not right! The resistor leads need to be long enough to allow the resistor body to sit about a half inch above the socket. Some people like to bend the leads over so the resistor is not sitting directly above the socket but that means you need adequate space around the socket. I like to do it this way...
http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg
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That's not right! The resistor leads need to be long enough to allow the resistor body to sit about a half inch above the socket. Some people like to bend the leads over so the resistor is not sitting directly above the socket but that means you need adequate space around the socket.
You want the screen R up in the air above the socket because of heat?
That's why I run the other end up in the air some. Like 22.5 to 30 degrees angle. I would think 3w metal oxide R's should be fine.
Most, if not all Traynor's have their chassis sitting with tubes up, like Marshall's, not tubes down like Fenders. So a lot less heat in the chassis. Even Traynor combo amps. They have a wooden shelf in the cab that the chassis sits on that divides the speakers from the amp section of the cab.
Just solder the R to pin 4 1st. Keep the lead ~1/4". Then run the R over the top of the socket, you run that R going to pin 6 up in the air a little, on an angle, so it's lead will be a little longer.
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Thanks for the expert feedback. Sometimes I need to be spoonfed. :worthy1:
Checked my stash of supplies and don't have much in the 3W metal oxide bin. Will need to order some before I can complete the updates.
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470Ω/3W metal oxide is not the only option. Marshall used a lot of 1K/5W screen resistors on their 50 watt amps.
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470Ω/3W metal oxide is not the only option. Marshall used a lot of 1K/5W screen resistors on their 50 watt amps.
It's better, gives the screens more protection. (The 1K/5W.)
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I assume you are refering to the 5W 1k Xicon wire wound resistors like Hoffman sells for Marshalls? I can check and see what I have in wire wounds.
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Is it necessary to jump up in watt rating when going from Metal oxide to wire wound? If ordering Metal oxide, is it better to just go with 5W rather than 3W (if space is not a concern)
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it's just easier to find 5w wirewound than 3w. either should be sufficient.
P = IČR. 5W = IČ * 1kOhm. IČ = 5W / 1kOhm. I = sqrt (5W / 1kOhm) = 70.7mA. EL34 max screen current 50mA so by the time your resistor is dying your screens have melted
3W/1kOhm is 54.4mA, might act as a 'fuse' for the screens but if you're relying on resistors as 'fuses' it's rather poor design
3W/470Ohm it's 79.9mA