how much filtering can a 5Y3 take?

[phsyconoodler]

The reason I'm asking is that I have a Mesa Lonestar special on the bench and the filtering is 2-220uf caps in series,for about 110uf total.
  The amp and quite a few other ones I've worked on,eat the 5Y3 rectifier tubes for lunch.
  They last about a year or even less and then crap out and blow the fuses.
You can't use just the diode rectifier as the 'progressive linkage' only goes through the 5Y3 when the amp is set for 5 watt or 15 watt oepration.
   I know that a Sovtek 5Y3 is not a 'real' 5Y3 but even so it should not have 110uf as filtering.
I think it's a design flaw but I'm waiting for a lashing from Mesa about this.
   It seems every Lonestar I get in has the same issue.

[Dave]

Many people have brought amps to me that some "tech" had done a cap job on and then the amp wouldn't work right. Normally what I have seen is that people try to cram in 80-100 microfarads claiming that it'll give them more filtering and a tighter bottom end, but what it usually gives them is an arching 5Y3. I have used 40Mfd, but I think that is even a little much.

Dave

[Joe6v6]

Most of the tec sheets say 10 or 20uf (*input cap), I saw one that said 32uf max. I have used 40uf in this position and although I was a little worried there seemed to be no ill (short term) effects. 110uf seems way above what would be acceptable.   .    Joe

[tubenit]

32-40uf, I think is about max with a good one.

Having said that, one can always use a lower value for node A (to OT) and a higher value for node B (power tube screens).  I have done this on a Carolina Blues Special with a 6AX5 and it sounded fine to me.

With respect, Tubenit

[phsyconoodler]

Ok,I got a service update on the amp.There are a couple of resistors on the board near the filter caps that have to be removed and that's supposed to help with the 5Y3 issue this amp seems to have.Early models need to have these resistors removed.I did that and the amp is up and running again,but time will tell if it lasts.
  To me 110uf is killing these tubes.

Frankly I can't stand the sound of this amp,but I have to fix them so there you are.

[FYL]

Capacitance is only a variable, as are plate supply resistances and raw voltages. All three should be considered when designing a valve-based power supply, as they determine max transient as well as steady-state current - a 5Y3GT is spec'ed at 440 ma design center max steady-state and 2.5A max peak. If you significantly exceed these values, the valve self-destructs.

In a nutshell: low supply R and high voltage => low capacitance, say up to 20µF for a real 5Y3GT; highish supply R and medium voltages => higher capacitance, say up to 47µF or so. Anything between 16 and 33µF is usually safe.

[tubeswell]

I too have used 40uF on a 5Y3 with no discernible problems, but I wouldn't go much higher than that. 100uF is way too high. 16-20uF is the norm

[HotBluePlates]

What did those resistors do? What did they connect to?

There are a lot of factors that go into determining how much capacitance you can use with a rectifier. There are about 18 straight pages in RDH4 about selecting and using rectifier tubes, and calculating what's happening. That's probably more pages than was spent on how to design an output stage.

It's all about how much current is flowing through the rectifier, especially during current peaks. And it's a lot more current than you'd think. The RDH4 design example has a amp that draws 125mA from the power supply, and the peak current through the rectifier is nearly 400mA. Of course, RDH4 also shows that there is not a lot gained from increasing the main filter cap much above 16uF (it draws one curve on a particular graph for caps that are 16-40uF, where other curves are shown for 4uF and 8uF).

The only way to keep from popping rectifiers when you have too much capacitance is to either lower the capacitance or increase the power supply impedance, usually by putting resistors in series from the high voltage winding to the rectifier plates, in order to limit current.

If the resistors you removed could have been between the PT and the rectifier (as in when the PT windings are connected to the p.c. board), then it is probably a step in the wrong direction. Hard to know without more info.

It is noteworthy that the typical condition in the 5Y3 data sheet is for 350vdc, 20uF cap and 125mA dc output, with a supply impedance of 50 ohms per plate. If you went through the RDH4 procedure using those numbers, you'd find this is a limiting condition that would pop rectifiers if exceeded. But you could go up on the capacitance if the supply voltage were reduced, if transformer winding resistance were increased (or series resistors added), if current drawn were lower, or any combination of these.

[HotBluePlates]

Oh... and FYL's quoted 440mA steady-state corresponds to what I called "peak current". The peak I was referring to is the the peak value of current drawn during each charging pulse, and so you could call it "steady-state"... that peak is happening constantly, even if momentarily. This is as opposed to a one-off surge that the tube could handle, but not sustain repeatedly.

On another angle, I don't see what's gained by using a 5Y3 and 100uF+ of capacitance. The 5Y3 is fairly high resistance, so it's not as though slapping a big capacitor gives you good bass; the 5Y3's resistance will tend to counter any improvement by limiting the peak transient current drawn.

[phsyconoodler]

The resistors in question are connected to pin 3 of the power tubes.There are a set of 100 ohm 1 watt resistors right beside them.They are some sort of cathode bias resistors that are part of the progressive linkage design.There are no details on the linkage and it's schematic is a closely guarded mesa secret,I suspect,because it does not show it on the schematic.
  As far as I'm concerned,a good VVR kills it anyway.I do not like the way these amps were designed.

[FYL]

Yup. The 440 mA steady-state figure translates to app. 150 mA current drawn (say, a typical amp with a 6V6 PP and a few 12AX7's), while the peak value is related to the initial cap charge.

[FYL]

I do not like the way these amps were designed.

Contemporary Mesa amps are IMO a mess.

[echuta13]

AB764 Vibro-Champs and Bronco's used a 40uf cap.  It's more than a 5Y3 should have IMO, but it works.

[HotBluePlates]

Perhaps, but I can't stress enough that there are multiple factors to be considered. For example, we don't know the resistance of the PT. To find this, you should find the resistance of the high-voltage secondary, and add to that the value of the primary resistance stepped up by the turns ratio. This resistance acts to limit the current drawn by the rectifier.

In a big amp where you want excellent regulation, you keep this resistance as low as possible. But the big amp would also use a bigger rectifier that wouldn't mind the extra current. And if great regulation was needed, you'd have a fairly smallish filter cap, followed by an electronic regulator of some kind. So it still all would even out.

[FYL]

AB764 Vibro-Champs and Bronco's used a 40uf cap.  It's more than a 5Y3 should have IMO, but it works.

The 125P1B / 022772 PT shows quite a high winding R, with app. 5R pri and 340R total sec (170R per half) for a source R of app. 200R using 117V US mains.

[phsyconoodler]

If I owned the amp I would drop the filtering down or set it up to use a 5AR4.The amp sounds really stiff and lacks life.
  Some guys like them but after building my own they sound generic at best.Stiff,lack of harmonics,distortion is raspy,low wattage settings sound cheap.
  Then again if I did own it I would sell it as quickly as possible.
Yuck!
 

[whoops]

Hi all,
thank you so much for the great info.

I know this thread is old, but I'm restoring a Gretsch G6144 Reverb unit and this subject came across while analysing the schematic. Also the way the Filtering and resistor network was connected from factory is different than what the schematic shows.
I'm saying "from factory" because by analying the solders, component layout consistency and types of components  in doens't seem that any repair or mods were ever made to this unit.
Unfortunately when I started this restoration it was 1 year ago and when replacing the filter caps and following the schematic I saw the circuit was different so I changed it as per the schematic. I don't remember what it was, but I remember one of the resistors being connected in a different way.

The Filtering is done with 2x 20uf + 2x 10 uf caps. Schematic attached

I would like to ask you what do you think about the filtering arrangement on this unit, and if you think the filtering might be too much for the 5Y3?

Thank you so much for you help

[sluckey]

Looks fine to me.

[whoops]

Looks fine to me.

Thanks,
even after re-caping I still have some hum in the unit.

I have some chokes from amp builds around. Could I improve the filtering by replacing the resistor after the first filter cap with a choke?

[whoops]

I was googling more on the 5Y3 maximum Filtering values,
it was suggested in another forum that the max values for the first input capacitor would be 20uf for the 5Y3 and 32uf for the 5Y3GT.
I don't know if this info is correct or not but none of the datasheets I have for the 5Y3GT (RCA, GE) say the maximum value, what they refer to is "Typical Operation Conditions" and then 20uf is normally stated, well one of RCA sheets states 10uf. The only datasheet I have that states maximum value is the Brimar 5Y3GT spec sheet and it states 32uf as the maximum capacitance value.

So I'm assuming that 20uf would be typical/normal, 32uf the maximum advisable value. After that it' your own risk.



 

[PRR]

There's no "maximum value". As HBP says in this thread, "it depends".

"20uF" is on the datasheet because *at the time* that was the most likely value a designer would grab for a 5Y3 size job. Older sheets show "10uF" because at *that* time 10uF was about as much as you could buy in one lump.

[kagliostro]

If I remember correctly, Sluckey used 33uF cap after a 5Y3 without problems

and ... the "critical" value on datasheet refers only to the first e-cap, the second cap that follows the resistor can be larger

Franco


Merry Xmas

[whoops]

Thanks,
I didn't get it at the first read, but understand it better now.

It is noteworthy that the typical condition in the 5Y3 data sheet is for 350vdc, 20uF cap and 125mA dc output, with a supply impedance of 50 ohms per plate. If you went through the RDH4 procedure using those numbers, you'd find this is a limiting condition that would pop rectifiers if exceeded. But you could go up on the capacitance if the supply voltage were reduced, if transformer winding resistance were increased (or series resistors added), if current drawn were lower, or any combination of these.

[ac427v]

I'm thinking about a similar situation with a 5R4GYB and wondering if adding "Backup Diodes"  between the transformer and rectifier tube changes the input capacitor maximum rating?
--Craig

[HotBluePlates]

... even after re-caping I still have some hum in the unit. ... Could I improve the filtering ...?

Lots of things result in hum.  Can you be certain the hum is due to the (lack of) filtering?

The schematic implies input jacks which are not shorted when no cable is plugged in.  This could pick up hum out of the air; you'd diagnose by clipping a jumper from hot to ground on the input jacks and seeing if hum reduces.

This reverb unit has its own power cord.  Interconnecting cables between multiple pieces of gear with individual power cords can complete a large ground loop.  The solution (is this is the hum source) is transformer-isolation at either the interconnecting cables or at the power cords. Such isolation is a key feature of some loop-switchers that have facilities for output to more than one amp.

That's not a complete list, but at least something to consider.  The Gretsch has loads of filtering for what is a fairly light load on the power supply (2 preamp tubes).  They also already have 3 stages of filtering for the least-filtered tube stage...

[PRR]

> wondering if adding "Backup Diodes"  between the transformer and rectifier tube changes the input capacitor maximum rating?

No. (And there is no "max cap rating" without context.)

Adding a resistor does change things. But nobody does that?

[whoops]

Lots of things result in hum.  Can you be certain the hum is due to the (lack of) filtering?

No I can't. It's probably not.
I'm doing a complete circuit re-check and overhaul. Improve what can be improved for my needs.
On Filtering I asked in this thread because it was relevant to the topic discussed and just wanted to check with you guys what would be your opinion on the Filtering circuit Gretsch used.
Thanks HBT for your opinions and help,

As for hum I'm going to address different subjects one by one, filtering was just one of them:
1) using shielded cable were it's needed
2) test electromagnetic interference from the Power transformer into the reverb tank (the reverb tank is inside a card (paper) box and not metal box)
3) check the best positioning for the Heater Wires. test heater wires phase
4) check the best positioning for the wiring in general
5) Test different values for the grid stopper resistors

The schematic implies input jacks which are not shorted when no cable is plugged in.  This could pick up hum out of the air; you'd diagnose by clipping a jumper from hot to ground on the input jacks and seeing if hum reduces.

This reverb unit has its own power cord.  Interconnecting cables between multiple pieces of gear with individual power cords can complete a large ground loop.  The solution (is this is the hum source) is transformer-isolation at either the interconnecting cables or at the power cords. Such isolation is a key feature of some loop-switchers that have facilities for output to more than one amp.
That's not a complete list, but at least something to consider. 

Yes I will change the input jacks for something that shorts the input when no jack is inserted.
Although the hum and noise are with the guitar plugged in.
Noise is not from the setup (Guitar and Amp)

I'm quite familiar with ground loops, unfortunately I have to deal with that everyday being a studio and Live sound engineer.
I also checked for that with an isobox at the output and also just for the sake of testing lifting the mains Earth.

No worries HBP I will do a separate thread with these issues and my restoration progress in a bit, I'm just doing some more research and reading so when I do the thread I will just ask 10 basic questions and not 100.
I don't want to sidetrack this thread with my project.

Thank you all so much for your advice.

[davebolden44]

a lot of people convert hammond ao 35 chassis into guitar amps. the first filter on them is a 40 mfd. some of them have been going strong for 50 years

[tubeswell]

The 5F2A Tweed Princeton uses 32uF reservoir with a 5Y3, and that design is solid. A little bit of hum, but so what? 40uF? - no problems.


However, if you look at the 5F2, you will see a different (CLC) filtering arrangement with only 8uF reservoir, which works perfectly well in an SE amp to reduce ripple hum. Why did they change it? Cost of HT chokes got higher while caps got cheaper.


Will a 5Y3 work with 100uF reservoir? Sure, but not for as long as it would with 20uF or 40uF. The work required to pull the charge out of the positive pole of a 100uF cap is 5 x more than what is required to pull it out of a 20uF cap over the same time interval. This work is manifested in heat that needs to be dissipated by the 5Y3 plates. More work = more heat. More heat = quicker death.


Hum can have many sources, not just power supply ripple hum. In fact, its more likely that the hum is coming from other sources than the power supply ripple. Could be grounding, could be AC crosstalk from different parts of the amp. Could be RF noise or other electromagnetic interference. Could be a dodgy component (like a bad plate resistor).

[jjasilli]

IMHO, a good solution (per Dan Torres, BTW) is:


1.  Add a "pre-filter cap" of a small value which meets the tube spec sheets:  Tube rectifier > new small filter cap> small value isolation series resistor, say 10R > stock large 1st filter cap.  Now the Tube rectifier no longer "sees" the large cap.
2.  Failsafe mod:  A SS diode on ea leg of the AC supply to the Tube rectifier.  If the Tube rectifier fails by shorting internally the SS diodes help prevent destruction of other components.

[PRR]

> small value isolation series resistor, say 10R > stock large 1st filter cap.  Now the Tube rectifier no longer "sees" the large cap.

In this example, it "sees" 10 Ohms to some large cap. Say the first cap shoots up to 400V and the second cap is just beginning to charge. 400V/10r is a 40 Ampere surge.

Values like a hundred would be safer.

20u 100r 20u is a heck of a lot better filtering than one 40u cap. Just need to plan for the extra space, and consider if the few volts lost matters. (If it does, you probably want something bigger than 5Y3.)

[trobbins]

Some of the guesswork can be removed if PSUD2 is used to simulate a particular power supply and proposed diodes and capacitances, along with measurements of the power transformer winding resistances (as in posts #13,14).  The simulated levels can be compared to the diode datasheet for both hot turn on peak, and continuous peak current levels, to see if operation will not exceed ratings.  Sometimes that can show that larger capacitance values than stated in a datasheet can be used, as long as the circuit type and values used in PSUD2 are correct and appropriate.