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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Thu May 12, 2011 2:07 pm
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First off I pulled the suspect Princton Reverb chassis and the resistors (which were the original ones). They measured:

1.) 226K and 223K (with my Fluke 87-III DVM)


New resistors came in already. I tried the 200k-ohm's first. The TungSol reissued initially biased at:

1.) 25.6mA

2.) 26.4mA

After 15 minutes, they biased at:

1.) 27.6mA

2.) 27.9mA


The tone was very noticeable. Weaker midrange than the hot-plated TSRI. I played several songs that I'm familiar with tonal response from my Epiphone SG-400. It kinda sounded like I was playing through a hi-fi amp---very sterile.

The song that really had a different tone was the old on "Sleepwalk." It lacked the warm harmonics of the slides, double stops, vibrato, and bends. They lacked the rich harmonic I'm used to hearing from this amp. Chordal work did not sound too bad. That is one of the best songs to try out guitar and amp settings--as it jumps from rhythm to lead work off one guitar. I used Satriani's version.

When I put in the Hytron 6V6GTY. All the harmonics and richness came back. Even with the 200-kohm resistors. They tested at:

1.) 30.2mA

2.) 30.7mA

At the start.

However, the tonal difference was quite amazing. The midrange and all the harmonics came back immediately. I didn't even bother to measure the bias, after 15 minutes.

After 5 hours of trying the TSRI with the 200-k-ohm resistors, the tone was not getting better. Even using TS-9 tube screamer and MXR-90 in front of the amp.

Therefore, I decided to go back to using 220k-ohm resistors. However, when I pulled the TSRI tubes out to do the swap, one tube's centering pin broke into 4-5 parts and fell into the chassis. Just not having good luck with this tube. So waiting for centering pin adapter from AES. That way I won't do the un-thinkable while swapping tubes.

BTW... the amp has new mil spec Amphenol octal sockets on the rectifier and power tubes.

I put the Hytrons back in. They biased at about 33-34mA. The thing sounds like a Princeton Reverb.



I am sorry to report this. Esp after all the effort Jim made to check those red plated tubes. These honestly had a much better tone from the get-go. I wish they did not go red. They sounded MUCH better. Leading me to believe that this tube is meant to be biased hot. (Just my opinion).


Specifics of the amp:

1972 Silverface Princeton reverb.

1.) New 20/20/20/20 525 VDC cap can. F&P from AES.

2.) All new Sprague 25/50VDC bypass caps on the input/gain stage/EFX tubes.

3.) New bias supply cap (100mfd/100VDC), rectifier (UF4004), resistors (metal oxide 5%)---27K-ohm and 100K-ohm
5%.

4.) New 1K-2 watt and 18K-2 watt resistors in the power supply section.

5.) Put into a custom cabinet with 12-inch Celestion Gold Alnico 8-ohm, 50-watt speaker. No doping.

http://www.youtube.com/watch?v=5c8nanTCPz0


Sorry about the initial news. Will keep you up-to-date, as tubes break-in


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Thu May 12, 2011 2:17 pm
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Disappointing news to be sure, Steve.

I doubt I'll be seeing any of those TSRI 6V6GTA's in my future.

:(

Arjay

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Thu May 12, 2011 8:58 pm
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Retroverbial wrote:
Disappointing news to be sure, Steve.

I doubt I'll be seeing any of those TSRI 6V6GTA's in my future.

:(

Arjay

The ones I had are out of the amp and back in their boxes.....I have more than enough American made tubes to take a chance on a RI tube.
I hoped they were some good ones because they're a helluva lot cheaper and readily available....oh well,someone else can experiment.


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Thu May 12, 2011 9:59 pm
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It'd be naive to think that Tung-Sol isn't aware that there are less-than-happy campers out here. Hopefully, they'll correct what ails this tube and subsequent production will meet our expectations.

Arjay

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 10:33 am
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Ok... I replaced the 220k-ohm OEM resistors with Caddock 220-Kohm (1% model MK-132's) resistors. I'm going to go for hot biasing TSRI tubes again and see what happens. As the original "red-plated" one did sound very good until they went red.

It sould be that the OEM resistors were drifting up, as the amp was being used. Caddocks are known to be pretty heat stable.

Certainly sounds very good with either Hytron 6V6GTY or RCA 6V6GT. And bias at 32-35mA, with plate voltage of 435 VDC (at idle).


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 11:47 am
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Is that the mA reading for both tubes Cathode current, or just one tube?

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 11:54 am
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I'm not trying to be smart here...but why are you going to all this trouble? :?


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 12:51 pm
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Because I get a lot of 6V6GT amps in for repairs. And my stash of NOS 6V6GT's is getting a bit low. I'd like the tone of this TSRI 6V6GT. Minus the red plating, of course. Best new 6V6GT to come around in awhile. Very close to original RCA 6V6GTA tone.

JJ's are going through some bigtime QA issues. If you get a good pair of power tubes or rectifier, consider yourself lucky.

If swapping out those two 220K-ohm resistors with 1%, high temp stable resistors does the trick. It'll be worth it. I'm looking for tube that will take abuse and last. Maybe not to the extent of the NOS 6V6GT's, but at least a few years of good service.

I'm hoping that farting around a bit, will help others out there looking for cheaper new tubes. As the prices of NOS is starting to go up-&-up.

For Shimmy, edit: 22-24 mA per tube.


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 12:56 pm
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BMW2002Ti wrote:
As the prices of NOS is starting to go up-&-up.


+1

I'm down to eight or nine NOS bottles myself. If a good new-production tube emerges, it helps to keep these old Champs, Princetons, and Deluxe Reverbs on the road.

Most of my clients are not down with spending $65 for a pair of vintage 6V6GT's. The re-issues are a much more palatable option.

Arjay

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Fri May 13, 2011 5:44 pm
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Thanks....I too would like to see a very good 6V6 and also 6L6 stable new production tube.....I didn't know you repaired amps BMW....it makes sense.
thanks to y'all I can see results,and hopefully this tube situation will improve....because...they ain't making 'em here anymore And I don't really think much of the GT GE 6L6's...and not really sure they're made in California...could be though.

btw....those NOS Tung-Sol 5881 tubes in the Super cost me $175.....ooooooowwww!
never spent anywhere near that!...BOHICA!


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Sat May 14, 2011 12:56 am
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Rebelsoul wrote:
btw....those NOS Tung-Sol 5881 tubes in the Super cost me $175.....ooooooowwww!


OUCH!

I'm still holding one pair of NOS brown-base Tung-Sol 5881's for the day that a tweed or a brownface follows me home......

:mrgreen:

Arjay

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Tue May 17, 2011 9:22 am
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Going to get another pair of "hot" Tungsol RI 6V6GT (testing at 32-34mA for the pair, in test machine). And try them out on the PR test bed. The one I replaced with 220k-ohm (1% tolerance) resistors. And redid the entire bias power supply with 1% resistors, new cap, and new UF4004 diode.

See how it goes, after several hours of heavy use. As this tube does not sound good with cold biasing. The "red plated" pair sounded great, until it went so red that it started distorted way too early in the volume (just like signs of too hot biasing).

Report to follow.


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Post subject: Re: Bad news about a pair of TungSol 6V6GT reissued tubes.
Posted: Sun May 22, 2011 6:52 pm
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I put the new matched pair of TSRI 6V6GT's into my silverface Prinecton (same amp as before). They biased to 32.5 and 30.8mA, after only 15 minute warm-up. Only was able to play about 2 hours so far. But, sounds very good. Warm midrange. Reminiscent of good NOS 6V6GTA's. No red or orange spots on the plates. Will recheck bias after a few more hours of playing.

Will update, as tubes get more hours.


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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Sun May 22, 2011 7:14 pm
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:shock: 14 watts at idle! I wouldn't be surprised if these don't last either. I wonder how many watts they run while playing. :?: You could use an adjustable bias instead of changing the control grid resistors to reduce the idle current. :idea:

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Last edited by shimmilou on Sun May 22, 2011 8:24 pm, edited 2 times in total.

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Post subject: Re: BAd news about a pair of TungSol 6V6GT reissued tubes.
Posted: Sun May 22, 2011 7:32 pm
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Shimmy, I agree. But, when I set the bias back down to 20-25mA level, it sounds pretty bad. It's the initial bias readings that I didn't really give them much chance to warm-up. Will check them in a few. Get back to you.

BTW... How does adjustable bias affect the tremolo/vibrato on this amp---as it works off the bias power supply?


Thanks!


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