Use a 6L6 or EL34 in place of the 6V6

[tubeswell]

The application for the 1K resistor in place of a direct wire from pin 4 to the 22K decoupling resistor and 2nd filter cap turret is to allow me to use an EL34 in my amp in place of the 6V6, since the EL34 has the extra supressor grid.

The suppressor grid is not a substitute for a screen grid. It is just a tiny grid at cathode potential right next to the plate, and its there to stop the loose 'lectrons from bouncing back off the plate. So you are using the 1K as a screen grid resistor. In that case I would use at least 10W, probably even 20W. But even 470R would probably be okay. YMMV. The screen just needs to be a few volts below the plate for maximum effect. You measure the voltage dropped across the resistor and the actual measured resistance of the resistor. Then the power dissipated is the voltage squared/divided by the resistance. Then you double that answer to be on the safe side.

I have already jumpered pin 1 to pin 8 on the octal socket. If this is the correct way of allowing the amp to use an EL34 then I would guess the resistor should be at least capable of 15W. Is this correct?

You just hook pins 1 and 8 up in parallel. You don't need a resistor between them.

The 500R pot is a Bourns and is rated for 2W. Is this sufficient? I am attempting to allow myself a way to adjust the bias for any power tube I may use. Do you have another suggestion? Can this be done? I can purchase a 5W Omite rheostat if necessary. I have not seen any smoke but that doesn't mean it's not getting hot.

Try it and see how you go.

The power rating of the resistor should be about double what the resistor actually sees. eg. if it is a 470R resistor and it sees 30V at the cathode, then the power burned up in it is: (30V/470R) x 30V = 1.91W (say 2W) therefore the cathode resistor would need to be about 5W to be safe. If you have two resistors in series then the total power dissipated across them with be shared between them proportionately according to their relative resistances.

Can you explain how to measure the cathode idle voltage? I am assuming it is just the voltage with all tubes in and the volume control at zero. Is this correct?

Measure the DC voltage between the cathode and chassis ground with the tube at idle (no signal)

[brodude]

tubeswell:

I am sorry if I have confused you with my lack of knowledge. I am only trying to make this amp capable of using different power tubes. My understanding is that there is an extra grid that needs to be addressed for an EL34 verses the other tubes. I am not trying to make it a screen grid unless that is what needs to happen to get it to work.

I guess my question should have been: How do you modify the octal socket to accept an EL34, a 6V6, and a 6L6? I have a properly rated impedance rotary switch from the 2K, 4K, and 6K primary leads from my OT so I can select different primaries. The common from that switch goes to the turret connection for the second filter cap and the one end of the 22K decoupling resistor. The primary common of the OT is connected to the plate, pin 3. I am then told to install a 1K 5W resistor between pin 4 and the common connection at the rotary switch, which is the other side of the primary input to the octal socket. Is this the correct way to allow me to use different power tubes in this SE amp?

I am sorry for all the questions. Maybe I should have stuck with just the simple 6V6 amp (Princeton) but I figured I wouldn't learn anything that way. You have been extremely helpful and I can't thank you enough. Maybe if I get to NZ or you come to the States we can meet and I can buy you dinner or something.

I did not have a resistor between pin 1 and 8. I was in reference to this 1K resistor to allow the use of an EL34. Should I just stick with 6V6's and 6L6's?

I will take your advise and upgrade the bias pot. Will I not need to adjust the bias using this pot if I change to a 6L6 or EL34 from a 6V6? Is this necessary? I do not want to have to take the amp apart to change resistors.

I do have the 500R pot and and a 20R in series for biasing. I also have the recommended 25 mfd cap in parallel.

Thanks again,
Darrell

[tubeswell]

tubeswell:How do you modify the octal socket to accept an EL34, a 6V6, and a 6L6? I have a properly rated impedance rotary switch from the 2K, 4K, and 6K primary leads from my OT so I can select different primaries. The common from that switch goes to the turret connection for the second filter cap and the one end of the 22K decoupling resistor. The primary common of the OT is connected to the plate, pin 3. I am then told to install a 1K 5W resistor between pin 4 and the common connection at the rotary switch, which is the other side of the primary input to the octal socket. Is this the correct way to allow me to use different power tubes in this SE amp?

Hi Darrell

Are you able to post a schematic? (You are losing me a bit with the description - sorry)

All you need to do for the EL34 is wire pins 1 and 8 together. The other pins shouldn't need any changing, unless you want to add a screen grid resistor to pin 4, the value of which could be anything between 100R to 4k7 I guess, depending on how much you want to lower the screen voltage. (But beware the power rating)

6V6 and 6L6 will run happily in there with pin 1 and 8 wired together, but the characteristics of the screen will be different if you put that extra screen grid resistor in there

Will I not need to adjust the bias using this pot if I change to a 6L6 or EL34 from a 6V6? Is this necessary?

No usually you can just change the B+ by chucking in a different rectifier tube, and the same 470R that works for a 6V6 will work for a 6L6 or EL34. (The voltage across the cathode resistor increases as the B+ increases, taking the bias up accordingly). However it you want an adjustable bias using a pot in series with another resistor, then maybe use a small 2-5W pot (say 200R) on top of a 5W 390R-470R resistor. That way the pot will see (at the most) only ~1/3 of the total dissipation, and the fixed resistor will see the rest. I note that AX84 KT88 SE power amp uses 1k 2W in series with 100R 5W - which is probably fine allowing for the fact that a KT88 is a really robust tube and the plate voltage in that amp is quite low for a KT88, so you would want to be able to run the bias quite hot. But I think that would allow to much bias sweep for smaller tubes (if you are intending to still be able to put 6V6 in there)

[brodude]

tubeswell:

Great to hear from you again. I hope I am not being a pest.

Here is an image of my schematic: (I hope I did this correctly)


On the primary impedance switch the 2K is actually 2.5K on my OT.
On the secondary side of my OT I have two speaker binding posts. One is 8K and the other is now 16R. I have a switch that allows me to select between the two binding post outputs. If you suggest I have the 4K available I can rewire one of them. I have two 12" high end speakers. Both are 8K. I have 1/4" jacks and speaker binding posts on each speaker. This allows me to use the 1/4" jacks with a patch cable and run both speakers in parallel or without the patch cord and use each speaker individually. One is voiced for British and one for American tones.

The red rectangle shows where I was told to install the 1K 5W resistor so I can use an EL34.

Can you recommend any combinations for rectifiers and power bottles?
I have the following but can purchase others:
JAN 5Y3WGTA
Sovtek 5Y3GT
JJ GZ34
EH 5U4GB
Tube Amp Doctor 6V6GTB
Ruby 6V6GTBC
Sovtek 6L6WGC
Winged "C" EL34-WC

I forgot to mention that I have installed external test points for the bias measurement with the 1K resistor directly off pin 8 and before the pot and external test points for the plate voltage. I also have installed external analog meters for both so I can immediately see any changes or make minor adjustments.

The build I based this on is actually Angela's SE 6V6. I used all high end components and 16 uF filter caps. My PT is from David Allen and my OT is a Heyboer custom.

Thanks again,
Darrell

[tubeswell]

On the primary impedance switch the 2K is actually 2.5K on my OT.
On the secondary side of my OT I have two speaker binding posts. One is 8K and the other is now 16R.

You mean 8R and 16R?

I have a switch that allows me to select between the two binding post outputs. If you suggest I have the 4K available I can rewire one of them. I have two 12" high end speakers. Both are 8K. I have 1/4" jacks and speaker binding posts on each speaker. This allows me to use the 1/4" jacks with a patch cable and run both speakers in parallel or without the patch cord and use each speaker individually. One is voiced for British and one for American tones.

Run the OT at 4k for 6L6/EL34 and then you can plug the 16R worth of speakers in to the 8R tap to run the OT at 8K for a 6V6. (Otherwise you can probably run the 6V6 at 6k)

The red rectangle shows where I was told to install the 1K 5W resistor so I can use an EL34.

That's fine

Can you recommend any combinations for rectifiers and power bottles?

Run the 6V6s with the JAN5Y3GT

Run the other tubes with the GZ34, or maybe try the 5U4G (if your 5V winding is rated at 3A) with the 6L6 - see how mushy it gets

When you power it up, test it with no tubes first and see if you have high voltage AC on the PT secondaries (with your meter between the secondaries and ground). Then switch if off, plug the rectifier in and check that you have a highish voltage B+ at the reservoir/first filter cap (it should steadily rise, but don't let it climb above the rated voltage of your filter caps). If the PT hums or buzzes wierdly at this point, switch it off immediately and check for an unwanted short somewhere between the B+ and the ground. If its okay, then plug the rest of your tubes in and watch carefully for smoke (with the back open), esp from that 1k screen grid resistor when you put that EL34 in (you might have to go up to 10W if it gets too hot). If it looks good, take some voltages (plates, screen, cathodes), and confirm your dissipation, with a range of rectifiers and output tubes.

2CW

Good luck and be careful

[brodude]

tubeswell:

Thanks again

Yes, I do mean 8R & 16R. I guess I was typing to fast.

Run the OT at 4k for 6L6/EL34 and then you can plug the 16R worth of speakers in to the 8R tap to run the OT at 8K for a 6V6. (Otherwise you can probably run the 6V6 at 6k)

This was confusing. Are you telling me to wire my speakers, if I use both together, in series to get 16R instead of parallel which gives me 4R? I have designed and built my speaker cab so I can use each 8R speaker independently or patch them together, either in series or parallel. One speaker is British voiced and the other American. On my amp I have two independent taps that can be wired either 4R, 8R, or 16R. Which two would you suggest. I have installed a switch so I can select between the two taps.

Based on the above can you please provide your opinion again on the combinations I should use for the 6V6, the 6L6, and the EL34?

In your last response I thought you said I would not need the 1K resistor to use an EL34 in this amp, just make sure I jumpered pins 1 and 8. Is this true? If your answer is yes then I will not install the 1K.

Thank you for the heads up on being careful. I am well aware of the voltages and currents. I do have a lot of experience with electricity just not building amps.

I have already fired up the amp and played it several times in the past few months with just the 6V6. I just wanted to make some mods so I can try other tubes and learn more from great people like you.

Peace & Happy New Year
Darrell

[tubeswell]

Are you telling me to wire my speakers, if I use both together, in series to get 16R instead of parallel which gives me 4R? I have designed and built my speaker cab so I can use each 8R speaker independently or patch them together, either in series or parallel. One speaker is British voiced and the other American. On my amp I have two independent taps that can be wired either 4R, 8R, or 16R. Which two would you suggest. I have installed a switch so I can select between the two taps.

If you want to hook up both 8Rs in series (to get 16R), then you can run both of them off the 8R OT secondary tap - to get a reflected load of 8K on the OT primary (for running 6V6); - or you can just run 1 x 8R plugged into the 4R OT secondary tap to get a reflected load of 8k on the primary (for 6V6).

But it is really up to you how you want to configure the OT/speaker load. If just that the 6V6 needs an 8k load resistance, whereas the 6L6 or EL34 will work better into a 4k load resistance.

In your last response I thought you said I would not need the 1K resistor to use an EL34 in this amp, just make sure I jumpered pins 1 and 8. Is this true? If your answer is yes then I will not install the 1K.

Jumpering pins 1 and 8 is a different thing from adding a screen grid resistor.

Try the amp with the 1k screen grid resistor and see what screen voltage you get. You may want to increase it to 1k5 or 2k2, 3k3, 3k9 or 4k7, or decrease it to 470R or take it out altogether, depending on your screen voltage relative to your plate voltage. Ideally you want the screen somewhere between zero and -60 relative to the plate. If the screen gets much above the plate, you will get more and more screen current, which could burn out your tube. (I have no idea exactly what value screen grid resistor you may want for the EL34. The stock amp doesn't have one - but it only runs a 6V6 - not much screen current there). However I can foresee that it is probably a wise idea for running the EL34 because they typically have higher screen curent. So try various values of resistance and see.

I just wanted to make some mods so I can try other tubes and learn more from great people like you.

Shucks, I'm not that wonderful. But merely insanely addicted to tube amps.

[brodude]

tubeswell:

I thought I would give you a few days break from my questions and in turn give me a few days to play with the amp.

I have not played a tube amp since the late 60's. Before I built this one I was playing my hand made guitars through my Boss GT8 into my mixing board and then through my studio monitors. This was very clean but did not provide the expression you can get with a tube amp. My plan is to mic the amp when I get it the way I think it should sound.

As you know this is a basic Princeton style amp with a few mods to allow the use of other tube types and high quality components.

I am not happy with the sound above the volume level of 3 and wondering if you have any suggestions. I can hear some distortion that is not pleasant to my ears. It is not from my speaker cab, as far as I can tell. I tried hooking up to my reconditioned Bose 601 from my stereo and it is still there. I can dial it out with my volume knob on my guitars but I am not sure that it is supposed to be there in the first place and that only lowers the volume anyway. Is this breakup and/or distortion and can I get rid of some of it? Is there something I can do to make it cleaner? I do not play metal. It also is not just associated with playing the bass strings.

It seems to be less when I plug into the second input which does not have the 1K resistor to ground. Can you tell me what the two inputs are for anyway? Is one better for humbuckers or pedals?

Also I tried the 6L6WGB with both the GZ34 and the 5U4GB but the voltage didn't seem to stabilize on the plate as I turned the volume up so I shut it down. My PT is a David Allen TP35 and is rated 320-0-320V, 180 mA, 6.3VCT@5A, and 5V@3A. I would think it could handle about anything I could throw at it. Is there something I am missing or need to do yet?

Over the weekend I tried to educate myself on what you meant by reflected load but could not find enough information. Is this also affected by the primary load resistance of the OT? If so, and I can select between 6K, 4K, and 2.5K, how do I calculate or know what output tap to use and what the speaker load should be?

When I stated "great people like you" I was refering to your willingness to assist and not just your expertise. Here in the States it is sometimes hard to find people that will share information and knowledge.

Regards,
Darrell

[tubeswell]

I am not happy with the sound above the volume level of 3 and wondering if you have any suggestions. I can hear some distortion that is not pleasant to my ears. It is not from my speaker cab, as far as I can tell. I tried hooking up to my reconditioned Bose 601 from my stereo and it is still there. I can dial it out with my volume knob on my guitars but I am not sure that it is supposed to be there in the first place and that only lowers the volume anyway. Is this breakup and/or distortion and can I get rid of some of it? Is there something I can do to make it cleaner? I do not play metal. It also is not just associated with playing the bass strings.

A single-ended tube amp has a certain rawness. And this simplicity is both good and bad. On the good side, what you put in is generally what you get out in terms of raw geetar tone, esp on lower vols. They are very touch sensitive - in terms of teh way you play your gat. However the circuit is pretty basic, and as a rule, you will not get clean sounds as you turn it up. The pre-amp is two basic cascaded tridoe stages of 12AX7 and the first stage tends to drive the second stage pretty hard and teh vol goes up. this distortion is passed to the output tube, which also has trouble turning a loud clean signal because the OT saturates fairly soon because of the constant current. I gather the fender SE champ and tweed princeton amps were intended for people on a budget, like your average student etc, and they are pretty basic amps. They have a certain charm and simplicity, and within the capability of the low vol setting you can get clean sounds. Or if you roll back your geetar vol with the amp vol up higher, you can get slightly different clean sounds. But that is an SE amp.

You can try extra filtering at the first reservoir/filter cap. This can take some of the sponginess out of an SE 6V6 amp with a 5Y3GT. Try 40uF (instead of 16 or 20).

You can also try a CLC filter - before the OT/plate supply node. The choke has to be rated to handle the maximum current draw of all the plates and screen(s) combined. For a SE 6V6 type tweed champ or tweed princeton, a 40-50mA choke is fine. For a 6L6 based one, a 120mA choke would be okay. For an EL34, maybe 150mA. This will increase the B+ voltages all-round, which will help clean up/refine/define things a wee bit.

A PP amp is a bit cleaner all-round, and fixed-bias is cleaner still than cathode-biased. Higher voltages are 'cleaner' than lower ones as a rule of thumb. Lower resistance plate resistors are cleaner than higher resistance ones as a rule of thumb. Slightly higher value cathode resistors are cleaner than slightly lower value ones as a rule of thumb.

It seems to be less when I plug into the second input which does not have the 1K resistor to ground. Can you tell me what the two inputs are for anyway? Is one better for humbuckers or pedals?

You mean 1M resistor to ground. The non-1M side of these Fender twinputs is a hi-pass filter. It has a bigger grid resistance (68k as opposed to 34k on the other side), and it has lower input impedance (68k as opposed to 1M). It reduces the guitar line signal before it enters the amps signal chain, which cuts out some of the cable EMI and also the EMI from not having a suitably shielded guitar pickup cavity (on the geetar body).

Also I tried the 6L6WGB with both the GZ34 and the 5U4GB but the voltage didn't seem to stabilize on the plate as I turned the volume up so I shut it down. My PT is a David Allen TP35 and is rated 320-0-320V, 180 mA, 6.3VCT@5A, and 5V@3A. I would think it could handle about anything I could throw at it. Is there something I am missing or need to do yet?

Try 6L6GC first and see what voltages you get. I need some numbers.

Over the weekend I tried to educate myself on what you meant by reflected load but could not find enough information. Is this also affected by the primary load resistance of the OT? If so, and I can select between 6K, 4K, and 2.5K, how do I calculate or know what output tap to use and what the speaker load should be?

Reflected load is the reflected impedance the OT provides back to the tubes, which is dependant on the impedance of the speaker to attached to the OT secondary. OTs do not have impedances as such, they have impedance ratios. For example:

- An OT with an impedance ratio of 1000:1 (Pr:Sec) will reflect an 8k load resistance on the primary winding when an 8R speaker load is hooked up to the secondary winding, or a 4k load on the primary when a 4R speaker is hooked up to the secondary etc.

So you can change the load resistance of an OT by changing the speaker impedance, dependant n the impedance ratio of the OT's Pri:Sec windings.

What's more, load resistance is not a specific target, but more of a ballpark spectrum. A single ended 6V6 can deal with anything between a 5k and 10k load resistance, with about 7k5 - 8k5 being 'ideal'. A single ended 6L6 or EL34 can deal with a 1k7 to 6k6 load resistance, with anything between 2k5 and 5k being 'ideal'. (My take on this is that this also depends on how hot you bias the tubes - hotter biasing means that more current is being carried through the tube, and therefore the tube will benefit from a higher load resistance to raise the plate voltage and therefore counteract the effects of hotter biasing, and vice versa. If too much current gets into the OT it will stop functioning as efficiently as a transformer and will 'saturate' - of course it is arguably somewhat desirable to achieve some extent of OT saturation in a geetar amp under certain performing conditions, but only in an optimum way - i.e.; when you want distortion of that kind).

Output tubes need a load to work (because that enables voltage swing, which is needed to make a signal), and they also need to work to use up the energy that is manifest at their plates. So load resistances at the higher end of the spectrum will make the output tubes do more work, and make the amp put out more volume (as long as the OT doesn't saturate), but load resistances at the lower end of the spectrum will make the output tubes hotter, and change the tonal characteristics (and make the OT saturate sooner).

Load resistances are typically specified on tube datasheets.

[brodude]

tubeswell:

Many thanks again for the information.

I will have to order a 40uF cap. I do not have one. Do you recommend anything other than the standard Sprague? Should I think about adding any other filtering before this one? If so, what do you recommend and will I need to move or add another choke. The choke I have installed now, between the first and second filter caps is a Hammond 1.5H rated for 200 mA. Is this too much choke?

Would you recommend replacing any other components or values of components per the schematic I sent earlier that would help with tone or improve performance? Any suggestions on tone or volume circuit? I love to experiment since this is my first one.

Yes I did mean 1M and all my handmade guitars have the PU cavities shielded with copper foil and properly grounded. The guitars sound exceptional, if I do say so myself since I made them from scratch and hand selected all the wood and hardware. I could send photos if you are interested.

I will get you voltages with the 6L6 installed. Would you like me to get the voltages using all the different rectifiers or one particular one. Do you need any other voltages besides the plate voltage?

I will have to re-read your explanation on reflected load again. I understand what you are saying but I am still trying to understand how to calculate it and how to select my primary impedance between 6K, 4K, and the 2.5K that I have available and then know which OT output I should use. Am I trying to make this too calculated or is it just really a matter of what sounds good? I have seen the load resistance on the datasheets but really did not know how it fits in the overall equation.

Peace,
Darrell

[tubeswell]

I will have to order a 40uF cap. I do not have one. Do you recommend anything other than the standard Sprague?

You can put 2 x 20uF in parallel. Nothing wrong with Sprague Atoms in my book. I hear a bit of complaining about them from some quarters now and again but I have not experienced any difficulty with them.

Should I think about adding any other filtering before this one? If so, what do you recommend and will I need to move or add another choke. The choke I have installed now, between the first and second filter caps is a Hammond 1.5H rated for 200 mA. Is this too much choke?

Is the choke before the OT primary supply node? (or between the OT node and the screen node?) 200mA should be fine

Would you recommend replacing any other components or values of components per the schematic I sent earlier that would help with tone or improve performance? Any suggestions on tone or volume circuit? I love to experiment since this is my first one.

Check out the bottom of this page for basic mod ideas:

Tube Terminology for Dummies

(No inference intended BTW ;-)

I will get you voltages with the 6L6 installed. Would you like me to get the voltages using all the different rectifiers or one particular one. Do you need any other voltages besides the plate voltage?

Yep - get the plate, screen and cathode voltages of all the tubes, with various rectifiers in. Write down the VDC to ground beside the pin #s. You should measure the cathode voltages on the 1/10ths of V setting (and the plates and screen on the hundreds of volts setting)

I will have to re-read your explanation on reflected load again. I understand what you are saying but I am still trying to understand how to calculate it and how to select my primary impedance between 6K, 4K, and the 2.5K that I have available and then know which OT output I should use. Am I trying to make this too calculated or is it just really a matter of what sounds good? I have seen the load resistance on the datasheets but really did not know how it fits in the overall equation.

Have a read of this:

Output Transformer Impedance

The impedance ratio (Pri:Sec) is the square of the winding ratio (Pri:Sec). (and the winding ratio is the same as the Pri:Sec voltage ratio).

So an OT with an impedance ratio of 1000:1 will have a winding/voltage ratio of the square root of 1000:1 i.e.: 31.62:1, or 36.62 turns on the primary for every turn on the secondary, and will give a VAC of 36.62VAC on the primary for every 1VAC on the secondary (in fact you typically measure the VAC off the primary when you hook up a low voltage variac to the secondary). And going in reverse - once you know the Pri:Sec VAC ratio, you can work out the impedance ratio. When you know the impedance ratio, then you will be able to work out what speaker load to hook up to the secondary, in order to give you the ballpark load resistance for the output tube you want to use.

On the other hand, if your OT has multiple primary taps (is that what I am hearing?) and one secondary winding tap, then rig up a suitable toggle switch to switch the different primary taps as desired.

[brodude]

tubeswell:

Hello again

If you go to my post in this thread on 1/5/10, (also see below), you can see the schematic I used and where the choke is placed. Is this correct? I have used 16uF caps instead of the 8uF's for the filters. I am assuming that I would put a 20uF in parallel with the first one on the right which is on the B+ before the choke. Is this correct?

I take no offense to your reference to the Tube Terminology for Dummies. That is exactly what I need even though I already know some of it. I even have a Rock Guitar for Dummies book even though I have been playing for over 40 years, on and off. I have no ego isues and a thirst for knowledge no matter where it comes from.

It will take me a few days before I can gather all of the voltages to send to you and until I order and install any new parts.

My OT is a custom Heyboer and I will have to email or call them to find out my impedance ratio. I will also look to see if this info came with the OT. If you look again at the schematic I posted (see below) on 1/5/10, on the primary I have an impedance switch to select between 6K, 4K, and 2.5K. On the output, which I do not show, I have the choice of 16R, 8R, and 4R.



Many thanks again for the information and assistance.

Peace
Darrell

[tubeswell]

If you go to my post in this thread on 1/5/10, (also see below), you can see the schematic I used and where the choke is placed. Is this correct?

Yep

I have used 16uF caps instead of the 8uF's for the filters. I am assuming that I would put a 20uF in parallel with the first one on the right which is on the B+ before the choke. Is this correct?

Yep

Now you need to measure the DC (idle) voltages to ground from pin 3, pin 4 and pin 8 of the output tube, and while you're at it measure Pin 1, Pin 3, Pin 6, and Pin 8 of the pre-amp tube. (When you measure Pins 3 and 8, you need to use the 1's or 10's of Volts setting on your meter to get the decimals).

You could also measure the DC voltages at the reservoir filter cap, the OT filter cap and the pre-amp filter cap.

Also measure the AC voltages across the heater winding and across the High Voltage winding

[brodude]

tubeswell:

Got it.

I will be back to you in a few days with the results.

Have a great weekend.

Peace,
Darrell

[brodude]

buzziness

tubeswell:

It has been a while. I had to go out of town on a large solar project for a couple of weeks and I just returned. I hope you are in good health.

I have not had a chance to order the extra filter parts yet because I am wondering if I need any other components after reading the articles you suggested and I have also not had the opportunity yet to take the voltages you suggested. I want to get it sounding good with the 12AX7, 5Y3, and the 6V6 before I move on.

I read another article on adding, not just another filter cap in parallel to the first stage, but adding a complete new stage using a 50 uF cap and a 300 ohm resistor to drop the plate voltage an extra 30V.

I have a buzziness that is there even at lower volumes and especially when my attack on the guitar is harder. It is not as clean as I would like even at lower volumes. It is not my speaker cab. I connected one of the Bose 601 speakers from my stereo to the amp and it is still there. I rebuilt these a coupole of years ago and they sound great.

After reading your suggested article from Aiken Amps on grid resistors I am wondering if this is what I need to add. I play mostly '60's rock and blues so I am not into much distortion. Is it possible to clean this amp up or am I waisting my time?

If you suggest adding these grid resistors, what values and where should I place them? Would it help if I also replaced the 1M volume control with a 2M?

Should I try a different preamp tube?

Regards,
Darrell