Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Mar Thu 21, 2019 6:51 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 37 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: 6EU7 tubes
PostPosted: Oct Mon 01, 2018 11:42 pm 
Member

Joined: May Thu 24, 2018 11:27 pm
Posts: 39
Location: NJ 08520
6EU7s, 12DW7/7247s and 7199s have not gotten any easier to procure, unless you are willing to pay the prices. These have become collectable tubes. The supply has dwindled and demand is ever-increasing. Folks who luck-out with a 6EU7 amp or preamp have only a few choices of brands and types of 6EU7 tube structures. Compare this with the amazingly large variety of types available with the 12AX7 family. If you like the large plate varieties of 12AX7 tubes, changing the 6EU7 socket wiring to accommodate 12AX7s becomes attractive. The only large plate variety of 6EU7 I have seen is the Sylvania type. Good tubes, but other earlier USA, UK and Euro large plate 12AX7s can surely sound good as well...or even better.....The RCA 6EU7 short plate type is another sleeper, almost as good as the short plate Mullards...

Similarly, the 7247/12DW7 tends to be limited in brands and internal structures. Sylvania and GE did make 7247/12DW7 long plates. The 1960s short plate Mullards are often preferred, but don't overlook the long plate Telefunken 7247...

As an exhibitor at a recent, large antique radio event, I was asked for 6EU7s and 7247s numerous times. Their demand is clearly increasing. 7199s are beginning to become priced like they are made with unobtainium. I am sure glad I have collected tubes for a few decades, because the times of "unearthing these collectibles" are now few and far between...


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Fri 05, 2018 5:33 am 
Member
User avatar

Joined: Nov Fri 10, 2006 12:24 am
Posts: 2210
Location: Thornhill, Ontario
Artcurus wrote:
...I have had to replace noisy 6AN8 in various equipment. (I have no love for this tube)...
I recently did some tests on about 25 random 6AN8's... for both noise and steady-state characteristics in DC coupled stages. They were quite variable. My conclusion: select good 6AN8's, don't do random tube changes. That said, I have a couple of power amplifiers using a DC-coupled front end (selected) 6AN8's that work just fine.
Cheers,
Roger

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Tue 09, 2018 2:35 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 11769
Location: Central PA 16801
has anyone ever done the socket rewiring or has ever used the socket adapter to use a 6U8 in place of the 7199 ?

if so, how did any of the tubes from the 6U8 family work in the circuit ?

I had quite a few 7199 tubes and a big Stromberg Carlson amplifier that used four 7199 tubes and the big beefy 6V6 (7591 ??). I sold it all for quite a pile of cash.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Fri 12, 2018 12:46 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5160
Location: Rochester NY USA
I rewired the driver tube sockets in a Stromberg ASR-120 amp from 7199 to 6GH8 (very similar to 6U8). DC voltages came out exactly as per the schematic, so it appears they're close enough. I anticipate doing the same on a Stromberg APH1030. Another missing 7199 for some reason...


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Tue 16, 2018 6:06 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8255
Location: Litchfield Minnesota USA
engineer wrote:
Artcurus wrote:
...I have had to replace noisy 6AN8 in various equipment. (I have no love for this tube)...
I recently did some tests on about 25 random 6AN8's... for both noise and steady-state characteristics in DC coupled stages. They were quite variable. My conclusion: select good 6AN8's, don't do random tube changes. That said, I have a couple of power amplifiers using a DC-coupled front end (selected) 6AN8's that work just fine.
Cheers,
Roger


I have four amps that use two 6AN8's as driver / inverters. I have had almost zero problems with those tubes. I wonder if those who are having problems are having those problems from possibly driving them hard by the factory's design. I wouldn't know, this is a guess that comes from such steady service in my case.

That said, since I use 8 of them I naturally decided to hoard for the long haul. I have plenty of NOS 6AN8A's.

I'm no longer using that amp that uses those 6EU7's . I went solid state for other reasons.

Mark D.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Wed 17, 2018 3:11 am 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 811
Mark D wrote:
engineer wrote:
Artcurus wrote:
...I have had to replace noisy 6AN8 in various equipment. (I have no love for this tube)...
I recently did some tests on about 25 random 6AN8's... for both noise and steady-state characteristics in DC coupled stages. They were quite variable. My conclusion: select good 6AN8's, don't do random tube changes. That said, I have a couple of power amplifiers using a DC-coupled front end (selected) 6AN8's that work just fine.
Cheers,
Roger


I have four amps that use two 6AN8's as driver / inverters. I have had almost zero problems with those tubes. I wonder if those who are having problems are having those problems from possibly driving them hard by the factory's design. I wouldn't know, this is a guess that comes from such steady service in my case.

That said, since I use 8 of them I naturally decided to hoard for the long haul. I have plenty of NOS 6AN8A's.

I'm no longer using that amp that uses those 6EU7's . I went solid state for other reasons.

Mark D.


Two Dynaco Mark III and one Newcomb AM/FM that used 6AQ5 x2. Every single one of these amps blew the 6AN8 at one point, and these units have been/were rebuilt


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 20, 2018 5:35 am 
Member

Joined: May Mon 14, 2018 6:14 pm
Posts: 207
I have a Bogen Challenger 35A PA, and a Curtis Mathes console that use the 6EU7.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 20, 2018 2:41 pm 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 11769
Location: Central PA 16801
yes, david bogen like those tubes along with magnavox.

does your 35 use 6L6gc or 7868 tubes in the output ? i had one and mine used the 7868.

it was one of the warmest yet robust sounding amps that i ever heard.

i love the 7868, but its price is out of control. also, they are run so hot in the amps and are usually weak when found barn fresh.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 20, 2018 4:23 pm 
Member

Joined: May Mon 14, 2018 6:14 pm
Posts: 207
I have the 7868. You all helped me solve a red plate issue I was having with them.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 27, 2018 6:39 pm 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 811
Dutch Rabbit wrote:
yes, david bogen like those tubes along with magnavox.

does your 35 use 6L6gc or 7868 tubes in the output ? i had one and mine used the 7868.

it was one of the warmest yet robust sounding amps that i ever heard.

i love the 7868, but its price is out of control. also, they are run so hot in the amps and are usually weak when found barn fresh.

steve


+1 on this. There's a huge difference between 7591 and 7868. My Sherwood S5500II that uses the 7868 blows my other Sherwood w/7591 out of the water.

It really shows up on movie soundtracks.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 27, 2018 6:44 pm 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 11769
Location: Central PA 16801
7868= my love/hate relationship

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sat 27, 2018 10:01 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4206
Location: Boston, MA USA
7868 and 7591 are identical electrically. Base is different — 7868 is Noval and 7591 is octal. My Sherwood with 7868s suffered two combustion events from shorted tubes. I have no love for those tubes.

-David


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Oct Sun 28, 2018 3:05 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 11769
Location: Central PA 16801
just like the 6BQ5, nearly all of the 7868 and 7591 tubes that i ever saw had the insides of the glass burnt.

no wonder, they were 6L6gc tubes in a package half the size.

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Jan Tue 01, 2019 12:12 am 
New Member
User avatar

Joined: Sep Sat 29, 2018 10:33 pm
Posts: 17
One of my favorite PP amps is a Magnavox 9302 which uses two 6EU7 tubes, one for each channel, AF amp/phase inv stages. The last 9302 I pulled from a 1962 console included a working 57-16-00 AM/FM tuner which contained most of the amps controls (power, bass, treble and volume) as well as a pre-amp stage, using another 6EU7 tube.

The 9302 actually is designed to house its own pre-amp stage, therefore there is an empty hole already labeled "6EU7" on the amp chassis and plenty of room underneath the hood to add the controls for it. Sooo... I removed the entire pre-amp stage from the 57 series tuner, including the 9 pin tube socket, 6EU7 tube, control pots and all associated components and transplanted them into the 9302 amp using the empty chassis hole and drilling new holes for the control pots. I also removed the 12 pin molex connector (umbilical connector for the tuner), added a fuse, a grounded EIC connector, power switch, LED pilot light and 8 new RCA inputs jacks (4 channels) with a new rotary 2 pole, 4 position input selector switch.

After recapping (and replacing a few resistors) and making a few cosmetic tweeks, I now have a fantastic integrated 8 tube amplifier (three NOS RCA 6EU7s, four new Sovtek EL84/6BQ5s and one NOS RCA 5U4GB recifier) that develops 30 watts (15 per channel) into a 4 ohm load. I tested many types of OPTs and came to the shocking conclusion that the original OPTs that were installed with the 9302 in 1962 had amazing frequency response (30Hz to 30KHz) and was more than enough "iron" to handle the 15WPC power output. I think people are too anxious to replace any OPT that doesn't have a steel bell housing, because they think it looks cooler, without testing them first, using the necessary test equipment of course (oscilloscope, frequency analyzer, etc.)

Note: I purchased the matched and balanced NOS 6EU7 tubes for $59.00 for all three.

_________________
"Failure may not be an option, but it is an opportunity"


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Jan Tue 01, 2019 5:07 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13604
Thinking that some tubes never go bad will get you in trouble. Sure small signal tubes fail less often than power handling types, but almost all eventually fail.

Sorta like the statement herer on ARF that tubes are seldom the problem, repl caps, check resistors etc. Many radios were retired because of some defect, probably a tube more often than not. I got some unrepaired radios from a closed TV/radio shop, almost all had some bad tubes.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Jan Fri 04, 2019 1:57 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 3443
Location: Sunbury, Ohio 43074
Seems to me we saw them in the TV repair biz.... but with so many tubes, and the cobwebs rattling around in my head, I would not swear to it .... it was a few years ago. :)

_________________
Preserving the history of electronics, one boat anchor at a time! :)
www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: 6EU7 tube
PostPosted: Jan Fri 11, 2019 8:09 pm 
Member

Joined: Dec Tue 09, 2008 2:49 am
Posts: 316
Location: Farmington , Michigan
At the bottom of the page are some other uses of the 6eu7.

https://www.radiomuseum.org/tubes/tube_6eu7.html


Top
 Profile  
 
Post New Topic Post Reply  [ 37 posts ]  Go to page Previous  1, 2

All times are UTC [ DST ]


Who is online

Users browsing this forum: manualman and 2 guests



Search for:
Jump to:  


























Privacy Policy :: Powered by phpBB