My Kingdom For A QUIET 7199!!

[zozoe]

Greetings, is there ANYONE selling a 7199 that is guaranteed to run quiet & be void of microphonics?
And something that will have been tested, & is returnable if not up to snuff? It's for a guitar amp.
Thanks folks~

[Stevem]

Which amp is this needed in, a Ampeg or a Sunn or a Dynaco?

[maxkracht]

https://www.tubedepot.com/products/tung ... pter-combo

Get the adapter, buy a handful of 6u8a's to audition.

[zozoe]

Which amp is this needed in, a Ampeg or a Sunn or a Dynaco?

hey Steve, It's for a Hilgen Victor R2522 single channel amp.... early 60's, out of NJ,,, most likely the same folks who made Sano, Giulietti, & the soon to be Ampegs.... very similar designs, looks, & handles... It's the second tube in, from left to right, facing the back of the amp..... That adapter thing with the 6U8A is noisier than the olde 7199,, NOT microphonic, but noisy.... The other 3 pre's are a mix of either 12au's or 12ax's, but with no known schematic, it's tough,,, 2-7591 & either a 5U4 or 5AR4,,, again,, tech time!! but I'll tell ya, with 3 ax7's & the crappy 7199, it's a friggin' Plexi killer.... I'm an expert at finding info online, but this one's kicked me in the arse.... First, I'll bring it to my tech, just to see what's up inside & then try to reverse engineer the appropriate sequence... thnx

[LOUDthud]

RCA has specs for noise on their data sheets for the 7199 and 7025. The way I understand it, you have to build the circuit, measure the gain, then measure the noise at the output with a true RMS meter and divide that by the gain to get the "Equivalent Noise Voltage Referenced To Input". Please correct me if I'm wrong.

7199: http://frank.yueksel.org/sheets/191/7/7199.pdf

7025: http://www.tubebooks.org/tubedata/HB-3/ ... 2/7025.PDF

[zozoe]

huh? ALL this is obviously way above my knowledge threshold,.. I play guitar & build custom pickguards,,, but what I HOPE you're saying is that my qualified tech could coax the readings he should be seeing & help get the order & value of the pre's straight,,, and also figure out which recto it should be....??
ॐ THANK YA'LL

[LOUDthud]

I'm saying we don't know if the problem is to tube, or a noisy resistor in the amp. Testing the tube(s) you have will tell us if any tube will lower the noise in the amp. Sometimes, hitting the suspect resistors with freeze spray will temporarily lower the noise telling you the resistor needs to be replaced.

Are the resistors in the amp carbon composition ? Those are the most likely to go noisy over time. Metal film 1% resistors are typically low noise and high reliability. If you are not skilled enough with a soldering iron, ask your tech to give it a try. Resistors in the plate of grid circuits are suspect.

[SoulFetish]

https://www.tubedepot.com/products/tung ... pter-combo

Get the adapter, buy a handful of 6u8a's to audition.

I’m with you on this suggestion. There is abundant stock low noise, NOS 6U8A’s available at low cost. I think the consensus would be that a 6U8 operating noisier than most “NOS” 7199s is the outlier. Whatever time I spent trying to source acceptable 7199 replacement is time I will never get back.
Its like trying to find a quiet 6C4 for an SVT. I remember asking Enzo if he knew of a vendor who could supply reliably quiet 6C4s. She said the only way to get a 6C4 stay quiet, was to leave it out of the amp.