advice on my first guitar amp build/original design

[ALBATROS1234]

i have been doing my homework and studying schematics and reading everything i can, i finally got together enough materials to build an actual amp, i started with a preamp got that working, added a power stage which except for a hum which i estimate is from it being breadboarded and wires jumping all over it sounded ok, not great, and not very "tubey"  and it was cleaner sounding than i wanted ,i. figured adding a twin hi mu triode in between the first and last tube might get me a bit of overdrive. i put a volume after the first stage and before the power tube figuring it would act as pre and post gain control the last being like a master volume. when i wired it all up it was much louder including the background hum but there was no overdrive tone at all and there are a few quirks. firstly i can turn the late volume all the way up without problem but the early stage volume once it gets above half way it starts to crackle and distort in an unpleasant way, if the volume is turned up even more it honks and farts and no longer allows guitar tones to reach the speaker. i surmised this meant the signal from the first stage was to hot so i added a 300k resistor between the output of the 1st volume and the 1st grid of the twin triode. when i did this i got no guitar tone only a loud clicking oscillation. i thought perhaps too many ohms was causing the signal to go to ground  i went to 15k and its basically back to the original condition. basically with the 1st volume half way up or less and the second volume at any setting i get a fair sounding clean guitar tone with fairly loud background hum. was looking for help and suggestions on how to keep the concept but make tweaks to get a better tone and reduce noise. like i said some if not all of the noise could be from the fact that it is wired on breadboards with wires jumping all around and clipped together. i wanted to get a decent sound before properly wiring it up neatly soldered in a metal chassis etc. below is the schematic with tube compliment and some dc voltage readings at the plates and some of the grids from the pentode and power tube. thanks in advance for any replies.

[sluckey]

You have a lot of gain going on there!

Some suggestions...

V1... Change 300K plate resistor to 220K. Change 1.2K cathode resistor to 2.2K

V2... Change both 300K plate resistors to 100K. The second grid has no resistor to ground. This is a NO-NO. Connect a 1meg resistor from that grid to ground to correct that problem.

The above changes should help. However, if you still have a squealer with the above changes, I suggest completely removing the second half of V2, or just parallel the plates, grids, and cathodes and consider it as one triode.

Shooter should be along shortly. He has a lot of experience with single ended designs. Listen to him.

[ALBATROS1234]

thanks sluckey, i wondered about the grid resistor, i was kinda cobbling together schematic parts and pieces and i forgot that one, i was just looking in my rca tube manual and that resistor dawned on me ,perhaps im overloading the input of the first triode, theres no path to ground to get rid of the stopped up signal. why would reducing plate resistors give me less gain, i would think just the opposite as would it not allow more b+ to the plates?

[sluckey]

The first triode is fine. The volume pot is the grid resistor. You only need to add one for the second triode.

why would reducing plate resistors give me less gain, i would think just the opposite as would it not allow more b+ to the plates?

Smaller plate resistor will allow more B+ to reach the plate, or said another way, a smaller plate resistor will drop less voltage across it. This means the signal at the plate can only swing between B+ and some smaller voltage, ie, the signal voltage will be less.

[ALBATROS1234]

Oh I see what you're saying. I just assumed more voltages on the plate meant more gain. None thing that puzzles me is that I've learned through electricity/electronics theory that parallel circuits the voltage is constant and current splits. On my 7f7 (twin triode) I came off the power supply and used a wire but to tap 2 wires to each plate through the 300k resistors theoretically I should have the same vdc on both plates but I get 243vdc on plate two and 71vdc on plate one. They should be the same in my mind. Similarly I had an issue like this when building my preamp using a 6sl7 I would get like 160vdc on one plate and like 50vdc on the other. Why is it splitting unevenly when the wire and resistors leading to both are identical and from the same source split in 2?

[sluckey]

Why is it splitting unevenly when the wire and resistors leading to both are identical and from the same source split in 2?

It's true that the plate circuits are identical. But the resistor on the cathode determines the tube bias voltage which controls the current through the tubes. Since the cathode resistors are quite different, the current through the tube (and through the 300K resistors) will be quite different. The different currents will cause different voltage drops across the 300K resistor, therefore the measured plate voltages will be quite different.

[shooter]

Shooter should be along shortly

He left the frozen north for sunshine

I ran the 6F6 numbers on your schematic, if I wasn't distracted you're about 6.5Wdc.  the datasheet I have says that's close, maybe hot, but for SE we can run 100%, maybe more plate dissipation.

http://tubedata.milbert.com/sheets/028/6/6F6.pdf

You don't have a P.S. sketch, guessing both plate and screen(G2) are at the same tap?  not a problem per say, but I typically give G2 it's own tap.

once you go through what Sluckey suggested, plug-in your guitar, dime the master volume, 0 the gain pot, 5 all your guitar knobs, now go to 1 on gain, play, 2play..... where does the amp go from clean to the start of breakup?

[ALBATROS1234]

Ahhh ok this makes sense I may change my cathode bias to get my voltage higher on that plate as well. I'm at work now so I will tweak tonight when I get home and report back. Thanks so much guys.

Oh and grid 2 and plate on the 6f6 are from two different points with a resistor and filter cap between the 2 plus the plate on the 6f6 goes thru the output transformer as well before getting to the plate.

Thanks guys this is the kind of advice I needed. As  I am not following just one schematic and this is my 1st time building an amp. Besides I am cobbling together something from what I could scavenge. My total cost is around 50 to 60 bucks as is.

[shooter]

i surmised this meant the signal from the first stage was to hot

I suspect what you have is 28lbs of turbo-boost into a Yugo (3?) banger motor.  the poor power tube is cowering in the corner pleading NO, please, NO more !!!!

as you tweak, even on a breadboard, try hard and get lead-dress clean, you'll have more time for tweaks n less time "re-working".

[ALBATROS1234]

Ok I made some changes suggested but I don't have all the resistors to do all of the mods. What I did was changed the plate resist on v1 to 190k siince I didn't have a 220k I also change the cathode resistor to 2.3 instead of 1.2 that's as close as I could get . I also changed the 5.6k on the triode to 4.3k and I put the 1 meg from the grid2 to ground. It seems slightly better but the problem still exists. Next I bypassed the 6sj7 to see what just the twin triode into the 6f6 sounds like. I basically just took the wire that headed to the v1 grid and hooked it to the 1st triode grid. I gotta weird different issue.with the volume down all the way it was squealing. Sort of sounded like quiet feedback as if I were cranked and too close to and facing the speakers yet quite low in volume. If I turn it up 1/4 it stops and actually starts sounding fairly decent. Continue to turn it up and it gets quite loud and begins to overdrive in a pleasant way until I turn it even louder and it starts squealing loudly and tone gets crappy. So I don't know what to do. Without the first tube the tones in the mid to loud volume range show promise I just have to find a way to fix the vol off/low squeal and the cranked squeal but maybe I should can the 6sj7 and just do more of a 6f6/7f7 champish thing. A 7f7 is identical to a 6SL7 with a loctal base.

[shooter]

Guessing you don't have a scope?
This is kinda un-orthodox, look at the schematic, break it at IN 1, stick in something audio(mp3, etc), use the devices volume, set you amp volume at 10.  If you can get it to play ok there, move to In 2, repeat.

I'l try and hunt down some schematics that use similar configuration as you have, but it's 75degrees and I haven't been frozen in a week, soooo I might be slow

[ALBATROS1234]

i see what you are saying isolate it in sections to see where the squeals appear begin at power tube and if thats ok step back a stage. i will try that. its kinda weird that with 3 tubes it sounds fair but clean/no overdrive until the 1st stage volume is raised up halfway before it crackles and squeals and when i take the first tube and volume out of the circuit the problem changes to the squealing from volume off to 1/4 up then i get a fairly nice sound which gains volume and overdrive nicely until it gets 3/4 up then screams and sputters nastily. playing tube amps isnt new at all to me but working on them is. i love problem solving thankfully.

[ALBATROS1234]

i just did a quick check, i patch the input directly after the 52k resistor before grid 2, i went a little past the coupling cap and resistor because i was using my input coupling cap and 1 meg to ground. this actually sounds decent, no squeals at any volume, the volume was drastically decreased and there was virtually no overdrive even turned all the way up. so the problem or at least one problem has to be how the 1st triode is set up or how it is reacting with the second triode, the 1st triode is the one that only has 70 vdc on the plate as opposed to the 2nd triode which has about 109dc since i changed resistors earlier. do you think i should change the value of the kathode bypass cap on triode 1 or perhaps even take it off? i spose i can also change the kathode resistor as well, i am at a loss being a newbie and all, i will be stabbing in the dark, but you guys are definitely making the process easier. thanks for that.

[shooter]

this actually sounds decent

forward progress is good.
just pull V1 for now, move to V2A's grid, 70 & 109 are fine plate volts for now.  We don't care about guitar distorting yet, just a nice clean, everything works every time, then we can be creative.  do you have a spare 7F7?

[PRR]

Fender Champ plays OK with triode-triode. Even, in AA form, with a lossy tone control.

Pentode-triode-triode with high-gain values and no losses may be too dang much. Aside from over-whelming the poor 6F6, and likely sneak-back and oscillation, if you get it stable it will hiss like a porcupine in a bicycle tire until you dial-down most of the excess gain you put in.

Pentode-triode ought to be ample gain for any sane musician. Insane musicians (perhaps the more common sort?) will need very careful layout and tweaks to be stable with very high gain.

Remember that at the limit, what a 6F6 can do (similar to a 6V6), more *gain* does not make you louder. It's just a 5-Watt amp. More gain makes it easier to hit the 5 Watts, and easier to shove 10 pounds of stuff in a 5 pound bag (distortion: smashed potatoes, scrambled eggs, screeching harmonics).

[ALBATROS1234]

It was definitely something to do with the triode 1 cathode resistor and/or bypass cap I took them outt and put a matching 4.7k to ground like triode 2 has and it's acting like a good girl no more squealing. So I put the 6sj7 back in the loop and although better it still squeals if I turn it up beyond halfway. So screw the input tube it's a 6f6/7f7 champ. The tone is ok but I am certain I can balance it better. So I'm done for tonight tomorrow I'm gonna strip off all the unneeded components and re do it in a more efficient compact circuit without jumpers bouncing around like a rubber ball. That's when the tweaking will start. I may add a tone control etc as well.  Do you guys think I should add a negative feedback like a champ? I'm happy with the starting point now thanks to you guys. After I reconfigure I will draw another schematic and see if there are any helpful suggestions at that point. Thanks for all the help you saved me much time.

[ALBATROS1234]

oh and i do have a spare 7f7  i got this tube lot for 10 bucks with 2 6f6 ,2 7f7, 3 6sj7s and a handful of other interesting tubes. i want to play with compactrons. i am a weirdo i spose when i was learning it looked like everyone uses 12ax7/6v6 with single ended builds i want something that sounds unique hopefully. and what better way to learn than to make myself have to figure it out from scratch rather that just assemble a kit.

[shooter]

add a negative feedback like a champ

I typically don't build with NFB unless I have to, (squeal, osc...), I try n get drive so it just pushes the power tube "over the edge", there is a gritty, hard rock sound that seems to come from an SE pushed little to far

[ALBATROS1234]

I agree and will hopefully get some juicy overdrive out of this amp when I'm done. I'm not wanting heavy metal distortion but I would like to get something between Jimmy page and Blackmore with a touch of  Angus Youngs 70s sound when cranked. My main guitar is a Tele deluxe ri but i have a start and I'm building a guitar with p90 pulps. Thanks again for the help

[ALBATROS1234]

here is my latest config, sounds pretty damn good now, was a tad muddy so i added the .47uf bright cap. added bigger resistor to the screen grid of the power tube now the voltage is the same as the plate. it was 6 or seven volts higher, read somewhere it should be a couple volts lower, until i get some resistors i ordered thats all i can manage as i read it should be at least 5 watt type. also changed both cathode resistors and bypass caps. as shown in the schematic this thing rocks hard, actually i tad too hard as even at low volume there is some overdrive. if i crank it halfway its sounds like a mesa boogie, i mean this thing growls like you wouldnt believe, no need for any overdrive pedal whatsoever. if i take the 330uf off the second triode it sounds better for rhythm playing. i was thinking maybe i can put a switch to take it in and out, perhaps even a footswitch and use it as a lead boost. i was also wondering would i do better moving the volume in between the 2 triodes rather than having it at the end as a master volume. or should i add a second volume in between the two triodes and have a post and pre volume. also was thinking of adding a tone control although i almost want to leave it be as playing it strait with just the volume doesnt make me feel like i absolutely have to have one. also was wondering when the 330uf bypass cap is engaged is it too hot in the sense that i am harming the tube(s) or circuit. the xfrmr doesnt seemed strained thats for sure even with it on for a while it barely gets warmer than room temp.(who says you cant reverse feed an industrial control transformer) this has been quite fun i still need to take this thing from a breadboard with a bundle of jumpers and alligator clips to a permanently soldered, installed on a chassis,completed amp and i am already thinking what am i going to build next....hmmmmm this amp building/designing may be addictive.... thanks guys for the advice etc.

[shooter]

it should be a couple volts lower,

It typically runs a couple volts Higher since current is lower in G2 at idle

[ALBATROS1234]

Damn I don't remember where I read that. Maybe I miss understood. So I can leave it alone or do I go back to the 750ohm cathode resistor for the 6f6? Today I added a 1 meg pot with a brite cap in between the 2 triode stages. Love it much more control over gain.  If I crank the second/master vol I can use the first one to dial in some nice bluesy clean tones. Reverse that process  and I got nice crunch/overdrive. I have to get another pot to do so but im going to add a tone/ treble control as well. With my tele deluxe(humbuckers) its fine but with the strat bridge pickup it has a touch too much treble. Just been coming home each day and tweaking caps and resistor values. I feel really close to getting the most I can out of this circuit/tube complement.will be putting it in a chassis soon. Right now I am going thru a pair of 4ohm celestion 10 inches in series but I think I may get a 12 and build a small cabinet

[shooter]

go back to the 750ohm cathode resistor

put the 750 back n just use 100ohm, 2W for G2. 
the 750 is your "bias" R, adjust  it, calculate power dissipation, repeat till happy, or mad.
I'd shoot for 85 - 105% of max plate.  after each change listen also, you might like a cooler running "sound"

[terminalgs]

As for the squealing you had in your earlier version,  I know you've moved passed that but it sent up red flags of poor grounding, either at the cathode bypass cap or your B+ filter cap.   Be sure to check all your grounds with a DMM and make sure you read 0ohms between all ground leads of components,  not the blob of solder they are attached too, put the dmm probe on the lead of the resistor.  Even though that squeal issue is gone, if the problem was a ground issue, it might still be there.


another thing I noticed about your amp is the low B+ and plate voltage for the 6F6.  you'll see 250V on the plates of of a SE 6V6 (6F6's successor) on 1950's 3 watt tape recorder/players, not guitar amps.  Guitar amps (and PA amps of the 50's) generally put 315+ volts on plates of these type tubes to make 5W in SE amps or 10W-12W in push-pull.


On the following datasheet, it says under application "class A power power pentode... if a single 6F6 is operated at a plate voltage of 250V, the self-biased resistor should be 410ohms."  (although it doesn't say what the load is for that configuration,)


https://frank.pocnet.net/sheets/021/6/6F6.pdf


Another thing about the 6F6:  There are tubes from the 30's that are still highly regarded in HIFI and guitar amp world and there are tubes that are not.  the 6F6 fits into the latter category.    Building amps with odd tubes is a lot of fun, but ultimately you want a great sounding amp.  Swapping in a glass 6V6 gets you closer to that.  If you want to keep it odd, get the loctal version of the 6V6, the 7C5.    the 7F7 is a 6SL7 in loctal form, both are great tubes!


back to low plate voltage..  I'd like to see other comments on this subject from some of the gurus.. With the lower plate voltage, you might consider a pair of 6AQ5's in parallel ? 

[ALBATROS1234]

thanks guys, terminalgs as for the possibility of it being a ground or any other connection it is very likely as 75 % of this circuit is breadboarded. on a couple occations when i turned it on for testing i had no guitar signal and had to jiggle wires in the signal path to get it working. that will be amende when i solder it permanently to a circuit board. as for the tube selection it was for 2 reasons, 1. i have been studying hard and began to notice that there are many hi mu triodes and power tubes and i wanted my amp to have a unique tone and thought possibly an unconsidered/not often used combination of tubes may coincidentally work out nicely. also i am the type of person who asks why is it always done only this way? is there a better way. 2. i am limited on funds so buying a kit or trying to directly duplicate an established schematic wasnt affordable and i came upon a tube lot of 16 used tubes for $10, which had the 7f7s, 6f6s and a handful of other triodes, power tubes, pentodes(3 6sj7s) etc and i thought they would be great for experimentation. 

back to the amp, the plate voltage is due to the fact that i could not afford to buy a proper transformer, i am using an industrial control transformer that when i put 120vac in one side i get 2 sets of 230vac on the output or if i jump them together get 420vac. after going thru the bridge rectifier i get around 285ish when in split mode and 480 jumped. i was trying to get max plate voltage on the power tube which according to my trusty rca tube manual is 300vdc although i tryed to get it down it seemed impossible no matter how i tryed, i was afraid if i werent close to 300vdc i would blow the tube up. and it seemed entirely impossible to get under 200vdc for the preamp tubes which i have read usually like between 150-200. how do i get heater voltages you wonder. i use a 6 volt wall wart for each tube both are plugged into a switched power strip so when i power up i flip that on after 30 seconds or so i flip mains power which is a grounded 4x4 metal receptacle box with a standard light switch wired directly to my xfrmr. anyway best i could do was 267vdc on the plate, i was getting 273vdc on the screen grid and i could swear i saw it written it shoud be just below plate voltage so i added a couple 750ohm 5 watters as resistance.

 next the 750ohm 5 watt kathode bias situation is because i basically clipped the power section from a youtube video where this guy(d-lab) builds a se 6sj7/6f6 which sounded quite decent and i thought it might be a good starting place. secondly shooter i mispoke. i still have the 750ohm 5 watter on the kathode that didnt change ,what i did was add 2 other 750ohm 5watters in series on grid 2 in order to get my voltage below or in this case equal to the plate voltage. so should i take those out and/or add a 100ohm on the screen grid? i think i originally had nothing on th3 screen grid it looks like i even drew the schematic wrong that i posted recently. it was late sorry

i am going to carefully draw another schematic now that i have added the second volume and post it shortly. thank yoy both gentlemen i do appreciate the advice.

[ALBATROS1234]

ok so i took out the 1.5k of resist to the screen grid of the 6f6 and low and behold it sounds even better. i actually really like the tones i am getting, its very versatile with the 2 volumes, at high volume it never gets fully clean but if i back off on my guitar volume it cleans up quite nicely, with the post volume high and the pre volume low to mid it gets great bluesy tones. with the pre vol turned up and the post backed down this thing comes alive with plenty of crunch grindage available for classic 70s hard rock, step on a tube screamer an searing lead tones abound. i just love it. for something i cobbled together with bits and bobs laying around and a few focused purchases for under $100 i have a great practice amp that is all i will ever need in the house. if i wanted to i could upgrade to a 6v6gt or even 2 in parallel and get that much more although volume,this thing gets pretty damn loud as is though. i wonder what wattage i am pushing i have never had a tube amp below 50 watts. below is my schematic as is now. i plan on adding a tone control just for when i use the strat on bridge pickup its a little to much bite.

[shooter]

i wonder what wattage

Make some measurements;

Vk/Rk = I (voltage at cathode(Vk)/cathode resistor(Rk) yields series current (I))
now Pdis = Vp - Vk * I. (I'm ignoring G2's effect)
This gives you the DC power for the tube at Idle.

without a scope it's hard to figure the Audio power.  you can try to inject a 1khz sine wave at input, monitor with a meter set to VAC-rms at speaker, set vol to max, adjust the input signal till the meter value doesn't increase any more, take that value, square it, then divide by speaker value (4,8, 16 ohms)

[ALBATROS1234]

I have a heath 25mhz 4552 scope. I am not great with it I only know how to take basic measurements. I was fiddling with it in regards to this amp and I can measure a.c. and low voltage dc but when I tried to measure dc at the power supply etc it would surge up then drop down to the baseline on the screen then when I take the lead off the test spot and touch it again it wouldn't do anything. If I measure something else like a.c. I can go back and it would do the same surge up thing. I don't get it. I wanted to look at my dc to see how smooth it was or if I still had ripples if so I would evaluate filter cap size but I can't figure out how to get a measurement .guess I need to read up more on scope operation. I imagine my wattage must be between 4 and 7 watts because it's pretty loud.

[shooter]

between 4 and 7 watts

I think you're there, although I was perplexed my 1st time, finding I had 10W pdiss, and 3.5W audio and it was loud

find n download the users manual, study.  set up an easy experiment; measure all the batteries in your house, (DC).  then graduate to wall warts that are AC out (AC).  Extra credit: measure your amp, at the speaker, while you play a single note, clean, slide down the neck a ft-ish and play the same note.
I never use my scope for anything DC in this world. I do use it for all things AC

[ALBATROS1234]

yea i just wanted to see how good my filter caps were working, most dc wall warts i have tested are not smooth dc they still have ripple, some actually look like strait pulating dc as if there was no cap on it at all, i can only assume the cap was fried. i have a guitar cord that became crackly on one jack so i cut it off and play my guitar clipped to the scope and that looks neat as you play.i'm new to tubes(been reading about them a few months and built a 6sl7 overdrive last month) and this is my first amp. i know i need a signal generator and 8 ohm hi wattage load resistor to use a scope to trace problems on an amp ,i will get there. this was way too fun. i love solving mysteries and my other main hobby has been building intricate ww1 biplane models, taking a break from rigging and painting tiny details for a while.

[shooter]

wanted to see how good my filter caps were working

For those I typically use my meter, I set it to vDC, verify it's ~~close, then switch to vAC for the ripple.  with a SS PS I expect ~~~ 2vac at tap 1, ~<.2vac tap2, by the last tap I'm usually about 20mV or less.

my other main hobby

yup, I have a bunch I use as distractions between builds

[ALBATROS1234]

ok so i used your posted method to calculate plate dissipation.i got a measurement of 20.59v and divided by my ohms measurement of the kathode resistor which was 757ohm that result is plate current which gives me .0271994716 which i assume means 27.2ma. i then multiplied that times plate voltage which is meassured at 265vdc and i get 7.207... so i guess that makes it that i am at 7.2 watts? did i do that correctly? that seems high output as though right usually they call a single ended 6v6 amp 5 watts. the max plate dissipation according to tube data is 14w and the 6f6 says max Pd =11w. so if thats the case it seems that 6v6 5w amps could actually be higher if the bias is tweaked and could be closer to 10w on average. i expected 3 watts when i decided to use the 6f6, i guess its surprising to get over 7w. but this guy is sure louder than i expected and the schematic which i ripped the output circuit from claims 3w but only had a 6SJ7 as a preamp tube, i am using a dual stage 7f7.

do you have any suggestions on a tone control or should i go for it and do a treble and bass stack? where should it be placed in between the triodes or after the preamp tube completely? also whats the benefit of before or after the volume at each of the above pre and post volumes. ie do i was the tone(s) before or after the volume control and at which of the 2 volume controls should i place it for better control. also what value caps on a treble or bass control in my situation. sorry i have been mainly studying simple se circuits and many do not even have a tone control and when they do they are in different places and different values. i am pretty happy with the sounds coming from the amp except for the above posted need to cut a bit of treble when using my strat. should i just k.i.s.s. and just go with a treble cut tone. if so refer to above questions. i know i am confusing myself as i type. any advice will not fall on deaf ears. thanks

[shooter]

265vdc and i get 7.207

did you subtract your Cathode volts from plate volts then take that value *27mA

Your audio power will be max 50% of your DC power, it's the nature of class A

for a TS, start simple, look at a 1 knob champ, or Gibson 5watter, tweek the caps n see.  I prefer a linear pot for TS, but it's a personal flavor sorta thing

[92Volts]

Double check the 6SJ7-- the schematic and voltage measurement from "grid 3" look like the screen grid and suppressor grid are switched.

[sluckey]

Double check the 6SJ7-- the schematic and voltage measurement from "grid 3" look like the screen grid and suppressor grid are switched.

Only on paper. Besides, the 6SJ7 is long gone.

[ALBATROS1234]

no i did not shooter, if i do it becomes 6.6w. i got ya. in guitars which i have built its usually like you say audio(a) pot for volume and linear(b) for tone. i guess im gonna try to do the tone contol in between the triode. from what i read it drops gain so the triode after will pump it back up.

92 volts, i did in fact remove the 6sj7 a few days ago, perhaps you spotted why it was freaking out. thanks for taking a look.

waiting for parts now so i can permanently solder the circuit up. trying to decide if im going to make it as a head and get a speaker box or if i want to convert my existing crate g40c (solid state garbage which was given to me after hurricane katrina when i lost all of my possesions ) it is a 2-10 combo which i think i can strip everything, pop holes for the tubes etc. i would strip off the crappy carpet covering and put some for of new covering as well as a new grill cloth. i can get a piece of thin sheet metal cut to cover the control panel as i would have much fewer controls etc.

i was poking around in it and it has an accutronics reverb tank, its only a 9 inch 2 spring but perhaps i should look into adding a tube reverb.i don't see why not it seems to be the same as a spring reverb tank for a tube amp i just need to figure out how to inject the circuit, other than standard components a tube to drive it and a reverb driver transformer what else would i need? ill check around.thanks again guys

[sluckey]

A reverb tank that is suitable for a solid state circuit will most likely not work in a tube circuit. Input and output impedances will be wrong. What numbers do you see on that tank?

[ALBATROS1234]

I haven't checked it . I just figured whatever it is there has got to be a way to compensate /convert impedance. Wouldn't it basically be changing the ratio of the driver transformer. I am throwing out random numbers as an example but if a tube puts out 100ohm and the tank need 25ohm in a typical tube circuit that would be a 4 to 1 so maybe I need to source a 6 to 1 or 3 to 1 or what have you.perhaps the easiest might be to look at the schematic for the original amp and see if it's readable to duplicate that circuit on perfboard. There has to be a way. It just a case of is it more trouble and cost than it's worth or not to save  30 bucks on a reverb can. I have the tubes and other components I just need a proper transformer/driver.

[92Volts]

There are a couple ways to approach driving reverb with tubes. One is an output transformer... circuit design and the transformer may be similar to your power output stage...  primary of 5000 ohms (for EL84, etc) or more commonly 20,000+ ohms (for 12AT7 and other preamp tubes) with a secondary as low as 8 ohms. A cheap and easily available Fender-type reverb transformer is 22,000 to 8 ohms.

While SS circuitry "could" drive as low as 8 ohms without a transformer, the small amount of power needed makes a few hundred ohms convenient, which is too high for transformer-based tube circuits and too low for transformerless tube circuits (like cathode followers).

Adding a SS buffer to a tube amp is possible, if anything the biggest issue/annoyance is a lower-voltage, higher-current power supply for it.

[ALBATROS1234]

I got a weird problem. My amp have been working perfect for weeks and I have been using it frequently. It was in the chassis for the most part except the filament transformer was on the side plugged in a separate outlet from the high voltage transformer. Also when I mounted it the circuit board I made is on top of the chassis and the input/Output , power switch and volumes and tone pot were below so in originally left the wires long and wire nutted the 7 connections off to the side. In this config all was perfect . This weekend I had some time so I decided wrap it all up. First I mounted the small filament transformer and tapped the main power feed after the mains switch to the high voltage xfrmr in parallel. Secondly I mounted a terminal strip and took all of my wire nuts for the patches and soldered them to the strip. In doing so one of the tabs for my preamp socket broke.i soldered the pieces together.

The symptoms now are that if I turn the tone up past 3/4 when the gain is at a high setting it squeals like a Vietnamese car being tortured. Also if I pull the cord out of the input of the amp it also squeals. 2 things I found odd somehow the voltage to v1 jumped from 110ish to 140ish.i found a bad resistor in the filter section and fixed it but still I have squealing. When testing voltage it squeals when I touch meter leads to grid one tab on the socket. Any ideas or advice appreciated

[sluckey]

Inspect all the work you just did. Also look for collateral damage that may have accidentally happened. If you broke a tube socket you may have broken something else too, maybe a ground wire.

[ALBATROS1234]

Yeah that's what I was thinking. I poked around for a few hours yesterday o you think that the fact that now wires with high voltage are passing near the base of tube sockets and coupling caps could induce that into the circuit. Before I rerouted the wiresthe circuit board and wiring was away from the pots, tube sockets ,coupling caps and input. Now every thing is all together.

[sluckey]

Layout is important even in a simple amp.  Could be a factor. I'm still leaning toward something is broken. Show us a pic.

[ALBATROS1234]

I will when I get off work