6GW8s: T1 / T1 RVT Output Tubes: Going ... Going ...

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
The price of 6GW8s is rising in response to dimishing supply .... One of our members is considering re-wiring one of his T1s to accept 6BM8 output tubes. Out of curiosity, I did a sweep of e-tailers handling the 6GW8; results below. Unlike the similar 6BM8, no manufacturer is producing the 6GW8; all sales of 6GW8s are either New Old Stock - unused stuff made a long time ago - or used. Same situation with the 7189A (Magnatones) and 8417s (some Guild Thunderbasses); NOS pairs are $125 to $200. When the supplies are gone and unless EH or Sovtek decides to bring them back, once a set of T1/T1 RVT output tubes is shot, either the amp sits or you get hosed at the market. Point of reference; in the fall of 2006, I paid $30/pair for NOS 6GW8s.

The Tube Amp Doctor
http://www.tubeampdoctor.com/advanced_s ... 2&x=10&y=7 29.00 Euros/ea
Bioaudioworks:
http://www.boiaudioworks.com/index.php?cPath=88 none in inventory
The Tube Store:
http://thetubestore.com/nos-6gw8.html $28/ea NOS, none in inventory
The Tube Depot
http://www.tubedepot.com/nos-6gw8.html $29.00/ea
The Tube Man
http://www.tubeman.com/item567.htm $23.00, in stock
The Tube Shop
http://www.thetubeshop.com/tubeshp2.htm $15.00 used. Some NOS.
VacuumTubes.net
http://www.vacuumtubes.net/prices.htm $15.00 used. Some NOS.
eBay search sweep:
http://search.ebay.com/search/search.dl ... category0= various prices including $90 for a matched pair of Mullards
 

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
Thanks for the heads-up, cj.

It's going to make it interesting for those guys that are scooping up Thunder 1's and then trying to sell them for 800 bucks. :lol:
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Default said:
Thanks for the heads-up, cj. It's going to make it interesting for those guys that are scooping up Thunder 1's and then trying to sell them for 800 bucks. :lol:
So long as the subject of re-tubing doesn't come up ..... In a year or two, a pair of 6GW8s will be expensive. :shock:
 

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
6gw86bm8compmg9.gif


It certainly looks do-able, as there is minimal wiring changes.
You'd have to make circuit changes, there's no way around that. It looks from the specs, that the 6gw8 is a more studly tube.

Another way to go, is to punch another hole in the chassis and drop a 12ax7 in and rewire the sockets for 6bq5's.
The problem is that you're adding an additional tube and running the risk of overburdening the filament windings on the tranny. I'll have to look into the current draws.

If anyone happens to run across a T1 in non-collector shape (i.e. cheap) let me know. I'm willing to do some bench cobbling to see how much of a pain it is to convert these.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Fragment below is the 6GW8 output tubes from the T1 RVT schematic; no T1 schematic available. One 1/2 of one 6GW8 (V3A) is a gain stage and source of a dry signal to the reverb amp (A) when the reverb is switched off. The other 1/2 of the other 6GW8 is the phase inverter (V4A) driving the pentode sections of the 6GW8s, V3B/V4B. Email w/ T1 RVT schematic sent.


T1outputs.jpg
 

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
Gibson ga8t schematic here, has pins 6(plate, pentode) and 7(screen pentode) running at 255 and 245 v respectively. Pin 9 (triode 2) is running at 155 volts for the phase inverter.
Looks good, voltage handling-wise.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Other than the pinouts, the 6BM8 and 6GW8 are functional substitutes although the 6BM8 may not exhibit the same sharp cut-off attribute as the 6GW8; it's mostly a matter of keeping track of which relocated wire goes where.
 

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
Sharp cutoff may not be what we're looking for....(nudge, nudge, wink, wink)
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Right ... nothing unpleasant ... but there had to have been some reason for Guild to pick the 6GW8 for output over the 6BM8 which they used in the same RVT amp; would be nice if the grid resistors were mounted on a nearby wiring strip as opposed to directly on the pin .... we need some gut shots of the T1 chassis ...
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
So that's where the world's supply of 6GW8s went ... :shock: :shock: NZ-Bay; is that where they all came from? Impressive array!! Chassis shots of Coastie's T1 RVT:

View of power transformer, recitfier, primary B+, heaters, and bias supply and to the right, the output tube sockets:

chassis02.jpg


Closeup of output tube sockets, just above center and lower right. The bracket, if present on the T1, is removable. Due to length of the chassis, physical access to the output tubes is pretty good:

chassis05.jpg
 

coastie99

Enlightened Member
Joined
Jan 1, 2006
Messages
8,662
Reaction score
27
Location
Greymouth, West Coast, Newsyland
capnjuan said:
So that's where the world's supply of 6GW8s went ... :shock: :shock: NZ-Bay; is that where they all came from?

Yep; all bought on Trademe.

None were expensive; although I can't recall specifics, probably the most I paid was around NZ $30 for the 4 Miniwatts.

Here's the Trademe link if anyone wants to keep watch..............

http://www.trademe.co.nz/Browse/SearchR ... 0&from=fav

I'd be more than happy to act for anyone who might see something they want.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Thanks Coastie; what is the US$ to NZ$ exchange rate? 50 of ours fer each or yours?
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
I cruised the TradeMe links ... some impressive audio gear makes it way to NZ; everything from classic table radios to Class A amps. Also note the encroachment of the Chinese gear ... disposable is it?
 

sfIII

Member
Joined
Jun 22, 2005
Messages
386
Reaction score
0
Location
Jamestown, KY
Guild Total
59
I just "won" two off of Ebay... Can someone recommend a good/cheap tube tester.. I see a B&K on ebay for over $200... I think that would be a bit much... But looks like I would need to test 6GW8s, 6V6, 6L6 and the associated preamp tubes.
 

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
I can check my archived maggie/valco list- they seem to have strong opinions about testers.
I fear "good" and "cheap" aren't going to be found in the same auction though.

The problem with the cheaper testers is they test at wall voltage, not at 300+ volts like amps run at.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
The better eBay tube sellers always tell you which make and model tester they tested their tubes on. Apparently there are any number of ways to test the most critical characteristics of tubes and each tester mfr went their own way. Further, there are settings on each tester that vary from tube to tube and the switch positions for each tube type are in the book that accompanies each tester. No book means the tester is nearly useless.

Default is right; there aren't any readily available testers that 'stress test'; most test for heater current, shorts, and transconductance which is the characteristic of most interest and to be 'matched' in output tubes. The lower end models - like the one I used to have but let go ( :evil: ), just had the drugstore-style red and green zones. They are a little like boats; better to have a neighbor that has one than go out of pocket on your own.
 
Top