valco 510-11(spectator) build needs more gain

[ALBATROS1234]

i have been coveting this amp for a while after having seen numerous demos on youtube etc. this is my first clone amp plus my first time with a tube rectifier. i used a 6x5 instead of 5y3 because the pt i wanted to use had only 6 volt low voltage along with the 735ct(362-0-362) winding. i built it very close to original but it just had no bite or grit even when i cranked it fairly loud. with my previous 4 builds i used a master volume between the 2nd triode stage and power tube which allows me to crank preamp gain and turn overall volume down so i can get a nice overdrive sound at lower volume so i tryed this and it did help but not as much as i would like so i added bypass caps on the 2nd triode and power tube, this helped a bit but it could use a tad more. although cleaner than my taste i like the overall tone.what else can i do to give it a bit more bite?

also i got alot more hum than on my other builds. the heater tap doesnt have a center tap, should i make a virtual one? will that help? i think am gonna redo the heater wiring for a lighter gauge and use a drill to twist the pair which i havent done in the past but this seems to be the method of choice.

link to original schematic : http://www.oldfrets.com/Valco/Schematics/1950SuproSpectator.jpg

[dscottguitars]

I'm not much of an expert but I see you have 220K plate resistors and the original has 270K. That will change the gain by putting more voltage on the plates and more headroom. I don't know what your B+3 voltages are or how they compare to the original. Lower plate voltage equals more gain.

Another thing I have done with great success is put the tone stack with the master volume stage. That way you are driving the full force of the first stage into the second one without losing anything from the tone stack. That can have an effect on the tone control response, but you can change the values of the resistor and capacitor to get what you expect in tone response.

Hope this helps some...

Daniel

[ALBATROS1234]

Ah I forgot about that I didn't have any 270ohm so I used 220. I may have some 300 carbon comps maybe I will swap triode 1 since that is the gain stage.if still not enuff maybe I will try both. The amp sounds good really warm it just needs some bite. I tried a bright cap which helped on another amp but this one made it too thin even using different value ranging from 560pf to 110pf.

On another note I was wondering for a future single ended build instead of using one preamp tube while trying to squeeze max gain would it be better/smoother creamy od if I used 2 preamp tubes but used lower bias and maybe few or no bypass caps . Instead of flooring the one tube can you build gain like stacking bricks?

[DummyLoad]

looking at your schematic: do you really have the filament string wired as shown in series? IS the filament string secondary 19V?


--pete

[ALBATROS1234]

No not at all I just half assed that part after the fact that's why it looks tacked on to the bottom of the xfrmr. I saw it but didn't bother fixing it because it's kind of irrelevant to the question at hand.

Changing both triode plate resistors to 300ohm in place of the 220 did increase gain noticeably. I was thinking it's kinda there. I think a side part is I am not used to tube rectifier tone. It seems over all softer maybe a bit mushier. I have had guitar amps with tube rectifier but not in a very long time. Everything I built has been bridge recti. When I a/b with another amp that has the same preamp and power tube albeit different type transformers and a different style tone control it just seems the bridge rectifier amp is way punchier and has more bite. As I turn the volume up this increases. On the tube recti amp when crank it past halfway is starts to get slightly muddy and also whereas the bridged amp increases volume in a more linear way the tubes recti one doesn't increase in volume as much after half way up it just gets boomer and muddy. Should I put larger filter caps? The valco schematic had 10uf x 3 and my bridged one I used a 47 a 33 and a 10uf.

[terminalgs]

If you still want more gain, or you want to see the total gain that might be available, lift the ground lug on the tone pot.

[dscottguitars]

I think a 47uF on the first filter is good. When you say muddy, is it like washed out and not carrying the bass notes hard and clear? That would be a fix for that.

What are the voltages on your power supply rail? Lower plate voltage on the preamp will help with getting more distortion. The schematic on the original has larger resistor values and may have lower voltages for the preamp.

[DummyLoad]

built a variation of that ckt. about 11 years ago. ended up sticking a 6SJ7 out front - see attached.


--pete

[PRR]

Valco would have used 220K if they ran out of 270K.

VOLTAGES! Let's see what's not working right.

[ALBATROS1234]

At lower volumes  it sounds decent after the resistors change  my pilot light should come in ton8ght so o will install that and rewire the heater circuit to see if I can get the hum to quiet down. I still haven't gotten an answer on whether I need to make an artificial center tap for the 6 volt winding? Is it necessary?

Anyway after I fix that up I will take voltages and post them. My meter is on the fritz so I am gonna go get another one. Thanks as always gentlemen

[sluckey]

rewire the heater circuit to see if I can get the hum to quiet down. I still haven't gotten an answer on whether I need to make an artificial center tap for the 6 volt winding? Is it necessary?

yes

[ALBATROS1234]

Danke sluck

[HotBluePlates]

i have been coveting this amp for a while after having seen numerous demos on youtube etc. ... i built it very close to original but it just had no bite or grit even when i cranked it fairly loud. ...

I have an original one of these amps from ~1951.  My original doesn't have any real bite or grit either, though it may get slightly "un-clean" with the Volume & Tone controls max'd.

... i added bypass caps on the 2nd triode and power tube, this helped a bit but it could use a tad more. although cleaner than my taste i like the overall tone.what else can i do to give it a bit more bite? ...

Consider changing the tone control circuit to match the 5F2-A Princeton.

As it stands, the Spectator's Tone control mostly just makes the amp darker.  With the Tone control full-up, signal level from Volume control shaves the guitar's bottom octave by ~17% due to the 100kΩ resistor working against the 500kΩ pot.  Making the 100kΩ larger and/or making the 0.01µF smaller might help brighten things and make the tone control more pronounced, but just switching wholesale to the tweed Princeton plan will probably work better.

I have not tried this change, but seriously contemplated it for a while after I bought the amp.  My Spectator just didn't want to break up much & is dark.  After a while, I decided to let the amp be what it is, given the tiny cabinet & original speaker.  That's because mine is all midrange, and exactly cops the "Sleepwalk" sound when using my Tele's bridge pickup.

[ALBATROS1234]

Thanks for the reply. I knew it wasn't gonna sound like a Marshall but at least on the examples online it seemed to have a raw rasp of an overdrive tone that I like it sounded to my ear. On several online demos I imagine they were cranked to get max tone but that's not what was happening in my case. It seems like the louder I crank it it gets kinda mushy but not in a good way. This amp actually sounds best 1/3 up at the moment. I think there's something I have done wrong or something I have is not performing well in the situation. It's going thru 2 8inch celestion at 8ohm. The power transformer ran 2 6v6 a 6sj7 2 6j7 on a 6x5 so it should be able to run 2 tubes and it's the same output transformer which was hooked up to that very 6v6 the only thing is it was hooked up on this oval 5x7 thing as it was is a 1951 reel to reel. The 5x7 may be the way to go but I don't have a cabinet atm so plugging into my 2x8 is the best option .

[ALBATROS1234]

Actually my original plan was to build a spectator clone since I basically had the whole situation include above mentioned 5x7 cheapy speaker from 1951 so if I build a thin plywood combo for this chassis and that speaker to spectator cab specs it MAY come closer to orig tone I am looking for but I haven't got that far and the 2x8 is a known variable as well which is helpful during testing. I just expected something closer to the ones I have heard and when it sounded a tad anemic and got so flabby above noon on the volume with very little of the bite that attracted me to that amp I came to ask advice here.

[ALBATROS1234]

Something I thought about last night which is different. I did my input my usual way instead of following the schematic .I used a 56k with a 1meg grid leak. If you look at the schematic there seems to be no grid leak. How would this effect things?  I remember reading you need the grid leak resistor so if the grid gets stacked up there is a high resistance path to ground. Should I put a larger value it that position ? I have some 2.7 meg.

[sluckey]

If you look at the schematic there seems to be no grid leak.

Yes there is. Those 100K mixing resistors also serve as a grid leak resistor. They also serve as a 2:1 voltage divider for the instrument inputs.

I remember reading you need the grid leak resistor so if the grid gets stacked up there is a high resistance path to ground.

There must always be a dc resistance path between the grid and cathode. Otherwise, the tube cannot bias up correctly.

[PRR]

> If you look at the schematic there seems to be no grid leak.

When working, at the time, it would grid-leak via the guitar.

With the rise of stomp-boxes, you need a for-sure leak.

[ALBATROS1234]

i saw the divider but i usually put a 1 meg to ground after the pad/grid stop the input resistor in series with the 1st grid. like above in my schematic. i suppose the 1meg i put provideds a less attractive path the just tied to ground at the input. it seems i read if you put a larger value here it alllows less bleed off from the input forcing more electrons onto the v1 grid giving more gain.

[ALBATROS1234]

so i got my voltages for 6113(jan 6sl7wgt ) and 6v6:
triode 1. 6SL7 =136vdc      which gives me plate dissipation of 19 watts according to my calculation . using vk/rk=1 then pd=vp-vk *i
triode 2. 6SL7=161vdc
plate 6V6= 370vdc
screen 6v6=383vdc
kathode 6V6=18vdc 

i assumed the voltage would be pushing it for the 6V6 and i did notice it had a slightly more pronounced red glow than when in my other amp.i think these voltages wont work with 6V6  so i popped in a 6L6G and got the following.(besides a tad nicer tone)

t1=124vdc                    plate dissipation: 23.5 watts this is max according to rca
t2=150vdc
p6L6=330vdc
s6L6=357vdc
k6L6=25.5

i think the voltage is high all over, the triode values are the highest i have yet gotten usually close to 100vdc or 80vdc on triode plates. i can easily put a dropping resistor and get that better. and i think i can run those voltages that high on the 6L6 apparently i need to change my cathode resistor but do i go up or down? i think up would be best like 500ohm instead of 330ohm. i think this will get me to around 70% pd.

so do those fixes sound logical? add dropping resistor of 100k to 220kohm before i split to the cathodes and then change the kathode resistor to 500ohm?

if i am thinking right this should properly bias my 6L6 and give me more preamp od/break up and may = good tone.

well i guess its not a supro anymore it ended up being a tweak of mixed up schematics again.lol

[PRR]

> 6SL7 =136vdc      which gives me plate dissipation of 19 watts according to my calculation .

6SL7 is a 1 Watt tube.

Assuming you really have 256V dropping to 136V in 220K, you have 1mA which is 0.136 Watts, which is a very safe zone for 6SL7.

Not sure what you are not telling us.

[ALBATROS1234]

not the preamp tube i was talking about overall for the 6v6 using the formulas mentioned .  18v /330ohm =.054a  pd=370-18(.054)  which equals 19watts approx at idle right?

[ALBATROS1234]

been tweaking this guy trying to make it better and there has been noteable improvement. i changed to a tweed style tone and added resistors etc,see bleow schematic mods. the amp sounds good at lower volumes although not as much grit as i would like. it sounds great with a tube screamer used as a boost. vol set to unity with gain on 0 and tone at 9 oclock. which i could accept except the volume knob doesnt respond as i am used to . from 0 to noon it doesnt increase in volume as much as i think it should although the tone is good. once you get past noon the volume increases much more drastically for smaller increment and it starts to sort of break up. once i get 2/3 up it gets muddy and distorted but not in a good way as well as a bit of sqeauling depending on how migh the pre gain and tone are set. the sqealing may be that i still havent completely nailed down all of the ground wires as thats usually my last step to figure out a ground scheme that gives the least hum. there is usually a bit of background noise hum with any amp and this noise usually more of a hiss usually increases with volume. in this case its a hum, not super loud but its something i havent experienced yet as it does not increase or decrease with volume increase. its there at the same level whether the guitar and amp volumes are on zero or full blast.

i wonder if the muddyness is from the 6x5 not being able to handle the cureent but it seems one 6SL7 and 1 powermtube it should be ok. i have tryed 6v6, 6L6,5881 and 6f6 see bleow for voltages. they all seem to be biased to hot but i have tryed differnet kathode resistors and this seems to be the best tone. also do i need to get my screen voltages lower?

voltages:
6V6
plate: 377vdc     screen:381vdc   kathode : 17.6vdc
   
5881
plate: 339vdc    screen:362vdc    kathode: 25.3vdc

6f6
plate: 360vdc   screen:358vdc    kathode: 21.26vdc

it seems i forgot to write in the coponent values for the power supply, the 2nd resistor id 1.5k 5 watt and the 3rd is 33k 2watt an all 3 filter caps are 10uf

[ALBATROS1234]

also should i update the filter caps, in place its 10uf in all 3 positions just like the original valco schematic, i think i am supposed to use a no more than a 10uf with the 6x5 first position but should i add a larger one(s) in the second and third postions of the power supplu filter caps?

[sluckey]

I suggest connecting another 10µF cap directly to the 6X5 cathode and change the 4.7Ω to 100Ω. This will improve the filtering considerably and should reduce your hum noticeably.

[ALBATROS1234]

I added the extra resistor 4.7ohm 5 watr even though it wasn't a high value for that reason so add another 10 right at the start then this will effectively make it like 20uf of filtering on the 1st lug. Makes sense.

What about those high plate dissipation I know the voltage doesn't look crazy but when I punch the numbers up I am getting pd of 22 to 24 watts in each power tube change. That puts the 5881 at max but the other too way hot. Adding larger resistor on the power tube Cathode  didn't do much either.  Should I try to get overall voltage down and or drop the screen further..? Seems that in the rca  book I am exceeding screen values especially if I have a 6v6 in the slot. Perhaps this is just gonna have to be a 6l6 type?

[sluckey]

It's important to change the 4.7Ω to 100Ω. Then it looks like a 10uf-100Ω-10uf crc pi filter. Much more effective at reducing hum than just slapping a 20uf at the rectifier.

[shooter]

after you get Sluckey's changes, I would try a 500ohm for Rk, 470 is fine; there's my why;

Your Vk go's up, allowing a bigger swing before clipping, (more "headroom"), brings down Ip to acceptable levels, maybe.

[ALBATROS1234]

closest i can come to 100ohm in a hi watt resistor is 2 330ohm in parallel for 160ish ohms. i will try that plus the extra 10uf cap and raise the cathode resistor on the powertube. i want to say i put in a 500ohm or a 750ohm and it made the voltage go up into the 400s at the time i was still reserved to the 6v6 but when i kept seeing it too high i popped in a 6l6 and a 5881, the latter is whats prob gonna end up in the amp.

[shooter]

the voltage go up into the 400s

your cathode shoulda went on also, are you subtracting cathode volts from plate volts when doing the math?
I agree with you the 5881 or 6L6 is probably a better choice if you don't have one of the new 6V6's

[ALBATROS1234]

Yea I was subtracting voltage at kathode from plate voltage times current to get pd. I think I'm gonna stick with either the 5881 or 6l6 as I have 3 6v6 and all a pre 1960 ever so slightly used. The stage jumps higher with the 6v6s in there with the 500ohm kathode resistor it's still right under 400vdc and they are glowing super bright not quite red plating but maybe brownish orange plating lol.

So I did the mods the hum is gone so sluckey you nailed that one down. 500ohm power tube kathode seems fine but while I had the board out and I was soldering  I put some resistor values that I had used before like a 1.5k on the 1st triode and a 2.2k on the second that helped noticeably but I also reclaimed the 220k I put on the b+3 line to the triode plates cuz when I put in sluckey mods it lower the overall voltage which lowered the triode stages too much. Now I got as much gain as I could ever need but alas it is absolutely nothing like the original circuit I was trying to clone .it's basically a 6l6 single ended like I have been building the last 4.with a tube rectifier.
  At least I know it's not the 6x5 poor performance or that I was doing something majorly wrong it's just I liked the way the vintage supro spectator sounds but this transformer has too high voltage and plus I am omitting a huge part of tone by not having an original speaker in that style and size cabinet. Not to mention the output transformer is undoubtably a different impedance etc.The variables with those things added up to a cruddy sounding amp by just building the schematic as is in my situation with my speakers etc.

I guess I got it in the ball park now the rest is minor tweaks until it sounds good to me. I basically want to redo the tone control it something simple but not so interactive like the tweed circuit or the original supro which wasn't great.

[ALBATROS1234]

Ok so I did some tweaks just now and it looks like sluckey led me to one of the two fixes. First following links from my tone knob thread I looked a sluckey brilliance  circuit on his vox ac15 clone. First I thought .01uf was a high pass type coupling cap as I am used to seeing .05 .047 .02 on amp build so I default to this thinking I am passing highs. Pffttt yea not so much. Not sure which one rangong from.0047 to 100pf if not a multi coupling cap switch. Makes a HUGE difference. My whole muddyness when cranked problem gone.whole thing was a too much bass causing floppy muddyness.

Next thing is screen voltage. The amp originally was running higher screen than the plate as the voltages show.i stuck a 12k in and received a nice tonal result not drastic but so I checked voltage and it was just be low 350 and the plate 360. With the 33k screen dropped to 315vdc and plate jumps to like 375vdc. Then I went nuts and stuck a 220k and got screen down to 214vdc which pushed the plate to 400vdc and now it sounds great. So much better.

So how come No one told me how critical it is to have the screen that much lower than the plate. I always read in the RCA books things like max plate 375 max screen 250 etc. But in all four build I always had the voltages close in some cases above the plate voltage and no one ever seemed to think it was a possible concern. Well I tell you what somewhere today when flipping around reading about voicing perhaps Rob robinette page but I read screen should be 2/3 the plate voltage .from now one I will do this from the start.

Thanks guys as always. Next I think I am gonna tackle a 6j5/6sj7/el84 single ended.

[shooter]

Next I think I am gonna

......post your Vk number 
Just curious where you wound up powerwise

[ALBATROS1234]

 500ohms
Plate triode 1 114vdc
Plate triode 2 146vdc
Plate 6L6 424vdc
Screen 202vdc
Kathode 15.75
Kathode current .032ma
Plate dissipation at idle 12.86watts

These are numbers I am comfortable with so I just gotta find an appropriate tone control for my more than adequate high end bite.beffore the last 2 mods it sounded good but needed a kick in the shorts.