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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 08, 2019 2:24 pm
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Retroverbial wrote:
Outstanding. Those new bottles will feel right at home.

Arjay

I do hope so :)
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Wed Feb 13, 2019 1:30 pm
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:( Well I came home 7:30 PM and was quite exited to see my new old tubes, it's getting late, my tube tester is buried, ( Long story, has to do with my 23 year old son moving back in for a few month's and taking over the downstairs and I had to store stuff, he has recently moved out but I have not gotten to restore the downstairs yet), yet I need to try them. I remove the EH 6v6 from my PR and put RCA tube #1 in V5 and RCA tube #2 in V6, turn the lights down low and turn the amp on, the Mullard GZ34 takes it time to warm up as usual, I am looking for that warm blue glow from the tubes but only one glows blue the other show filament red, then a spitting sound happened, immediately I turned the Amp off. Than I replaced the EH back and all was quiet, I than took out my Euro-tube bias probe, it was too late to open the amp up to get statistics, and the bias probe is close enough. Checked one EH with the probe just to make sure, than checked RCA tube 1 in V5 and it showed 25 ma and than checked RCA tube 2 in V5 and as it was warming up this tube checked out at 25 ma than started spitting and while it was spitting my meter went to 37 ma down to 19 ma and back up to 35 ma., off went the amp, EH back in played a little bit, was bumming, couldn't get in to it, was getting late went to bed.
Sent the seller an email and said basically the same thing as above, seller was apologetic and is going to send another RCA close in value to RCA tube 1. I will just have to wait and see now in the mean time I will dig out my tube tester and check the old tube # 2 and than check it's replacement before I try it in the amp
My question is what make a tube runaway like that, and could a runaway tube be detrimental to the amp itself
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Thu Feb 14, 2019 9:17 pm
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Bummer Mud, it happens to us all sometimes. Sounds like the seller is a decent person though, so it may still work out ok.
If the tube is shorted it could do damage to a tranny or the bias resistor/capacitor. Best to recheck as you did with known good tubes. I would still double check the cathode resistor value before giving it the a ok just to be sure and if the tube socket has plate/grid resistors I'd check those also.


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 1:02 pm
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sfceric64 wrote:
Bummer Mud, it happens to us all sometimes. Sounds like the seller is a decent person though, so it may still work out ok.
If the tube is shorted it could do damage to a tranny or the bias resistor/capacitor. Best to recheck as you did with known good tubes. I would still double check the cathode resistor value before giving it the a ok just to be sure and if the tube socket has plate/grid resistors I'd check those also.

Thanks for your reply, yes it may still work out. Just for reference the amp is a Princeton Reverb. One anomaly I did not mention. After the runaway tube I returned the EH 6v6 back to there original spot and the tremolo was not working, I removed the Telefunken from V4 1/2 vibrato, 1/2 phase inverter, and put in a GE laying around and the vibrato was on again, than wondering if it took out my Telefunken I put the Telefunken back in and it was working seemed weaker than my GE, maybe it shortened the life, or maybe the GE is better in there anyway, but I never did an AB test on the two tubes so who knows.
Well on top of all that I had thought I put each tube in the right box so I would know which was which, and as soon as it was done something in me said, ya got it backwards, and thought about it and wasn't quite sure.
Dug my tube tester out, and this morning I checked out the RCA 6V6 on my Eico 666 and the tube I thought was the good one showed heater-cathode leak less than 500K more like 100K so that one did not get a merit test, the other one metered around 8meg, not new, I than did a merit test and it went past good.
:idea: I think when I am trying power tubes for the first time I may remove my Mullard GZ34 for a Ruby and pull all the Telefunken's and put in the GE's that I have a lot of.
Well I guess I am going to open it up, hopefully this weekend and put my meter to use before I go any further, and poke around on them resistors
Now another question if I can.. Would the use of a light bulb current limiter be the safer way to go when I am trying power tubes. I think I will build one this weekend.
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 1:43 pm
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For an unknown amp, I would use the current limiter.
If the fuse on your Princeton did not blow, your probably ok with out using the limiter. You can pull all the preamp tubes to prevent any stray signal from the output tubes.
I always drop in a cheapo rectifier tube that I know works, when I replace output tubes. I don't have a tube tester. Edit: I use a DMM to test pin2 to pin7, tube in hand. My RCA's measure about 3 ohms and my new EH's measure about 8 ohms. In hand, those are the only two pins that should have continuity and provide very low resistance.
The only tubes I keep in to check the output bias initially is the rectifier and output tubes.
Definitely measure the 27k bias resistor, the other power supply and plate resistors to include the PI/tremolo circuit.
It wouldn't hurt to use a limiter, if it makes you feel better.


Last edited by sfceric64 on Fri Feb 15, 2019 2:42 pm, edited 2 times in total.

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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 1:53 pm
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mud wrote:
sfceric64 wrote:

Now another question if I can.. Would the use of a light bulb current limiter be the safer way to go when I am trying power tubes. I think I will build one this weekend.
mud



Yes and yes

Image[url=https://flic.kr/p/27SjhSJ]c


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 2:18 pm
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sfceric64 wrote:
For an unknown amp, I would use the current limiter.
If the fuse on your Princeton did not blow, your probably ok with out using the limiter. You can pull all the preamp tubes to prevent any stray signal from the output tubes.
I always drop in a cheapo rectifier tube that I know works, when I replace output tubes. I don't have a tube tester.
The only tubes I keep in to check the output bias initially is the rectifier and output tubes.
Definitely measure the 27k bias resistor, the other power supply and plate resistors to include the PI/tremolo circuit.
It wouldn't hurt to use a limiter, if it makes you feel better.

I am kind of new with tube circuitry, but I have delved into it the past 3 years with much progress
I will definitely measure the 27K bias resistor, and the other power supply and plate resistors to include the PI/tremolo circuit.
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 2:21 pm
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stratele52 wrote:
mud wrote:
sfceric64 wrote:

Now another question if I can.. Would the use of a light bulb current limiter be the safer way to go when I am trying power tubes. I think I will build one this weekend.
mud



Yes and yes

Image[url=https://flic.kr/p/27SjhSJ]c

Yes that's the one. I have a 300w and a 500w incandescent lamp I will use.
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 2:30 pm
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300 W might be too powerful, not enough current will go into the amp.

Use a 100 watts


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 2:47 pm
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I edited my earlier post to show how I check my 6v6's before installing, since I don't have a tester.
That's all that I can do.


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 3:07 pm
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sfceric64 wrote:
I edited my earlier post to show how I check my 6v6's before installing, since I don't have a tester.
That's all that I can do.

That is better than nothing I had read about this test in the past
Thanks
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 3:19 pm
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stratele52 wrote:
300 W might be too powerful, not enough current will go into the amp.

Use a 100 watts

A good tip, but viewing Uncle Doug's video around 4:55 he say the higher the wattage the lower the resistance. Please let me know if you find error in any of this.
His videos are sometime very layman and goes over somethings as if speaking to someone with no experience at all but he does explain a lot
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Fri Feb 15, 2019 5:42 pm
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No faults in that video, that's exactly how it should function.


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Post subject: Re: RCA 6v6 Tube help
Posted: Wed Feb 20, 2019 4:02 pm
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sfceric64 wrote:
Definitely measure the 27k bias resistor, the other power supply and plate resistors to include the PI/tremolo circuit.
It wouldn't hurt to use a limiter, if it makes you feel better.

I dug into it this weekend and my bias resistor was within 10% tolerance, most of my plate resistors were with in 10% tolerance, one of the plate resistors has been out since I got it 117K ohm instead of 100K ohm, that may be the reason for an occasional crackle once, and maybe the slight hiss I get, but it hasn't really bothered me all that much, I will leave it alone until it does bother me when it gets worse, I have some Allen-Bradley 100k CC when that time comes.
Well the seller sent me a replacement RCA 6V6, and being my tube tester is now back out of storage I am using it. The two original tubes that I received and mixed up went into my tube tester and the one I thought was the good failed the heater-cathode leakage test, to the point I could not do a merit test, the other tube just passed by the heater-cathode leakage test, so I could do a merit test, it passed the merit test and when I installed it in my amp the spitting sound happened and I turned it off and pulled the tube. At this point neither of the original tubes are going to do me any good.
The replacement tube was perfect in every way, passed all the test and was over the top in the merit test, so I paid $50 for 3 tubes and received 1 very good RCA 6V6Image I had bought earlier 2 RCA Smoke glass 6V6 for $40 and when I installed them one was way hot and the other was not as hot, so the bias was off by too much and my amp did not sound so good. When I tried the strong smoke glass tube with the clear glass tube, the smoke glass was way strong I than put in the weaker smoke glass tube and I got good results V6 smoke glass 0.0207ma. x 400 Plate voltage = 8.2 Plate Dissipation and V5 clear glass 0.02206ma. x 400 Plate voltage = 8.8, ideal is 8.4, and the amp sounds pretty good. Image
So now when I look in the back of the amp I see the blues tube with that wonderful blue glow and the smoke glass tube that looks like an old jazz club, but together they sound pretty darn good, I will play them for a couple of weeks and than put in the EH tubes in the same spots they came from and be able to compare, as I do notice something different in the sound. I have used the EH since I got the amp in September and have gotten used to the sound, so at this point I am not sure which I like better.
mud


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Post subject: Re: RCA 6v6 Tube help
Posted: Wed Feb 20, 2019 4:14 pm
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I built the current limiter and used a 500w lamp as you can see with a load of a 60 watt lamp the voltage is 120.3 VAC
Image
and than I but a 60 watt incandescent bulb in the limiter I did not have a 100 W and put the same 60W load on it and I got 68.4 VAC.
Image
So the higher the wattage the less resistance I think the 500Watt lamp was the way to go
mud


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