AA764 champ last question

[catnine]

I had a 47 UF for the forst filter cap and due to posts around the internet this was said to be too much for a 5Y3 so I replaced it at the sacrifice of what sounded like bottom end and so highs I did not care for . Got rid of highs with a darker sounding JJ ECC83 preamp tube.

I didn't want to add a reister or other parts to drop the voltage to the first cap I don't really like patch work with extra parts.

From what I've gathered chokes make an amp sound looser , it this true . My amp is loud yet real quiet and my B+ is a bit over 360VDC on the plates JJ6V6s and I had to bias it with a 680 ohm cathode resister and it sits just at 13 watts IPD if my line VAC is at 119 and this varies down to 117.5 VAC.I statred out witha 1k cathode then a 750 and then a 680 and I still have bottom end with a weber ceramic sig 10s . My OT is a weber champ replacement 7k primary with a 4 and 8 ohm secondary tap and the weber is a 8 ohm . I can only guess what the 6V6 wants to see as per my plate and cathode voltage .

I look at tube charts but am completely lost , the amp sounds good . My gut tells me that an alnico speaker will warm up the sound more than anything else yet the price of one does not warm my heart . weber sigs have always been my choice and are not a lot cost wise. .

I use strats and heavy strings and it does seem to me for some odd reason in my 73 SF champ with a alnico sig 8s sounded better than the sig 10s I have now. AES has some b rated speakers like a jensen mod 10/50 cheap and I have used a mod 12/50 mod in a mm bass amp and it sounded pretty good but that was a pp 6V6 amp and there's a diffference.

I really don't know what I'm trying to say here . Maybe a champ is not the amp to produce SRV tone .

[Bruce / Mission Amps]

Undo the B+ lead(s) from lug 8 of your rectifier socket and solder a 2 watt, 33 to 47 ohm metal oxide resistor on lug 8 of your rectifier socket.
Snip the other resistor's lead off long enough to make a 1/8" diameter loop and from that end of the 2 watt resistor, feed all the B+ to your first (47uF) filter cap and the amp.
Plug your 5Y3Gt back in and use any first filter cap up to 68uF and you should be fine.
There is no patch work here to like or dislike and you will not being dropping more then a couple volts with a 47 ohm resistor!
You will however save the 5Y3 rectifier from the heavier current surge of the bigger filter cap on a cold start up... which is what can possibly wear out your 5Y3 prematurely.

[catnine]

Undo the B+ lead(s) from lug 8 of your rectifier socket and solder a 2 watt, 33 to 47 ohm metal oxide resistor on lug 8 of your rectifier socket.
Snip the other resistor's lead off long enough to make a 1/8" diameter loop and from that end of the 2 watt resistor, feed all the B+ to your first (47uF) filter cap and the amp.
Plug your 5Y3Gt back in and use any first filter cap up to 68uF and you should be fine.
There is no patch work here to like or dislike and you will not being dropping more then a couple volts with a 47 ohm resistor!
You will however save the 5Y3 rectifier from the heavier current surge of the bigger filter cap on a cold start up... which is what can possibly wear out your 5Y3 prematurely.

Thanks Bruce I will try that . I replaced the 47 uf 1st filter cap with a 30uf because I did not want to go down to the 22 uf , this is what F&T caps are at 500 volt rating. I have an extra 22uf cap I can parallel with the 30 uf or get another 47uf cap and place the 47 ohm 2 watt in series with the rect pin 8 to the first cap . I have a fuse in the B+ off pin 8 and then a standby switch then it goes to the 1st filter cap on the eyelet board , can I install this resister after the standby or is it better before the fuse? Is the resister there to not show a short while the 5Y3 is charging the resevoir cap

[Bruce / Mission Amps]

... can I install this resister after the standby or is it better before the fuse? Is the resister there to not show a short while the 5Y3 is charging the resevoir cap

Yes you can put it after the standby switch.
Well, yes pretty much, the resistor acts like a current "shock absorber" and limits the instantaneous inrush current from the rectifier to the first filter cap.

[catnine]

Yes you can put it after the standby switch.
Well, yes pretty much, the resistor acts like a current "shock absorber" and limits the instantaneous inrush current from the rectifier to the first filter cap.

Thanks Bruce :

I ordered the parts , I got another 47 uf F&T cap and a few 47 ohm resisters and as soon as they blow in I will report back so others can see the results.

It;s not that I use the amp on a daily basis but I didn't want to ruin a good NOS 5Y3 . I tried to measure the surge with a DVOM and did see a few second spike when the amp was turned on and it was higher than the cap VDC rating and I don;t have a stock of real 5Y3's sitting here . I used a sovtex 5Y3 for my 6G2/5E3 build but for some reason in that amp the higher voltage sovtex only raised the B+ by 5 VDC .

[catnine]

Do I have to use a 2 watt 47 ohm metal oxide resister or can I use a 5 watt wire wound 47 ohm instead?

[catnine]

I got this chassis from Allen amps and It's a real nice tweed style chassis tha I made this AA764 champ with . It has a standby switch hole marked , so even though I don't need a standby for a champ I used it because it was there and I hate marked face plate areas that are empty or have a switch that is just a dummy switch.

So what I am going to do is instead of the DPDT on /off in there now because this is all I had I have a SPDT center off and on one side place the 47 Ohm resister in series with the pin 8 on the 5Y3 to the B+ and on the other side run the B+ without the 47 ohm series resistor . And take out the low end loss 30 uf first filter cap and put back the 47 uf 1st filter cap I had in there to begin with and if there is some tone diff then I can switch it and if the 5Y3 blows and flys out like a bottle rocket I'll get another 5Y3 . The center off will be stand by . The amp worked fine with the 47 uf 1st filter cap and the NOS westinghouse 5Y3 for well over a year so far . I liked the bottom end the 47 uf 1st filter cap allowed and the 30uf is a change I can hear and bugs me to no end . I never thought a filter cap could make such a difference but it did and the highs that came on when I put the 30 uf in were unbearable .

[Bruce / Mission Amps]

Do I have to use a 2 watt 47 ohm metal oxide resister or can I use a 5 watt wire wound 47 ohm instead?

Sure you can use it.
The max current you'll get out of the power transformer of any <10 watt amp is probably much much less then 250ma. Probably closer to 100ma.
Your champ probably has a 70ma power transformer.
47 ohms and a 250ma load is, .25^2 x 47 = 3 watts.
100ma with the 47 ohm resistor would be 1/2 watt.
I'd be willing to bet a 2 watt resistor would last forever and some in your amp but there is no reason not to use a 5 watter if you already have it.

[catnine]

Sure you can use it.
The max current you'll get out of the power transformer of any <10 watt amp is probably much much less then 250ma. Probably closer to 100ma.
Your champ probably has a 70ma power transformer.
47 ohms and a 250ma load is, .25^2 x 47 = 3 watts.
100ma with the 47 ohm resistor would be 1/2 watt.
I'd be willing to bet a 2 watt resistor would last forever and some in your amp but there is no reason not to use a 5 watter if you already have it.

I've done quite a bit of reading on the internet about tube amps but I don't have any books other than one from Gerald Weber A desktop reference of Hip Vintage guitar amps.

I have to say where I get confused is when it comes to PT mA ratings and the load and actual mA draw placed on the PT .

My Champ PT is rated for 100 mA on the HT secondaries @330-0-330 VDC and a 6.3 rated at 4 amp and 5 volt rated at 3 amp and a extra sencondary of 300-0-300 VAC I got it from Weber and I guess it is designed for even a BF princeton reverb AA1164 with a 5U4GB.

My thinking is that the PT needs to be rated a bit above the total mA draw by the tubes combined and the seconday PT voltage .

So if you go with a low mA rated PT with too many mA's drawn the PT will over heat and fail sort of like placing a rect tube that draws 3 amps on a 2 amp rect 5 volt secondary .

Then there are wattage ratings determined by voltage drop across a resistor so a 22 VDC drop across a 5.1K is 22x 22= 484 / 5100 = .09490 x 2 =.1898 so here is seems that the old fenders with 1 watt dropping resisters were well more than enough . My 6G2/5E3 is the example above and this is what the voltage drop is across the 1st node in the power section . I used 3 watt flame proof dropping resisters in both the champ and the 6G2/5E3.

Where I get lost is, is it the actual mA draw of the combined tube compliment that would reflect the wattage rating of the node resistors or is there more to this where it's not that simple ? Is it the filter caps draw and current rush and the constant charging of the filter caps that make the 2 or 3 watt more reliable?

I have always gone with I guess over kill using flame proof 3 watt resisters in the filter section because this seems to be the norm these days and I have no doubt they will live forever .

[catnine]

Sure you can use it.
The max current you'll get out of the power transformer of any <10 watt amp is probably much much less then 250ma. Probably closer to 100ma.
Your champ probably has a 70ma power transformer.
47 ohms and a 250ma load is, .25^2 x 47 = 3 watts.
100ma with the 47 ohm resistor would be 1/2 watt.
I'd be willing to bet a 2 watt resistor would last forever and some in your amp but there is no reason not to use a 5 watter if you already have it.

Bruce :

I put the 47 uf 1st filter cap back in and added the 5 watt 47 ohm resistor between the fuse I have after pin 8 and the standby switch . I did bring back the bottom end and cut the highs and it was noticable.

I had the caps drained and then connected the DVOM to the B+ after the resister . I noticed if I leave the standby switch on play and just power the amp up I see the voltage start at about 450 VDC then drop down to 374 VDC within 30 seconds or less . If I drain the caps and then power on and wait then switch the standby to play mode the VDC is right away at 374 VDC B+ . There is a 2 vDC drop across the 47 ohm resistor.

I let it cool off and drained the caps and powered up again in the dark and saw no arching in the 5Y3.

[catnine]

JUst to add another question here

I have been reading about current ripple which is increased as you use a larger reservoir cap .

If I understand this correctly while you are playing through the amp there are duty cycles so the power the amp is running off are the stored power in the caps and the duty cycles are the PT and rect tube continually keeping the caps charged up .

Also since these cycles are short this is the reason you can get by with a PT of 223mA's instead of 1 amp . This is from lord valves site.

On this site also in big bold type is says not to exceed the tube rect max reservoir cap . I did put back the 47uf reservoir cap and as Bruce suggested a 47 ohm resistor between pin 8 of the 5Y3 and the B+ . Since I had a concern about shorting the 5Y3 since all I can find on 5Y3 is a reservoir max of 20uf . If I power up this champ AA764 build in the dark I see no trace of an arc in the 5Y3. My question is since the 47 ohm resister buffers the rate the 5Y3 charges the 47uf cap and the duty cycles come into play while playing does the reservoir cap just partially discharge between duty cycles?

The end result is a over heated PT and a destroyed rect tube.

After I play my Champ built for an hour above 6 the PT is barely even warm , nowhere near what is considered hot , I could keep my wrist on it all day . My PT is rated at 100 mA on the HT and with a 12ax7 and one 6V6 I am not even drawing close to that .

I may add a diode between the HT leads and the rect as a safe guard even though I have never seen this on any fender amp before. I read some do this and others never do . I had an 80's champ once and it kept blowing the fuse , not knowing a thing about tube amps I went into a guitar shop to get the fuse and told them it kept blowing so they sold my a 5Y3 , that fixed it . I have no idea how the 5y3 was shorted but it did blow the fuse as soon as I turned it on.