6L6 - Groove Tubes

Mark Herrick · Post by **Mark Herrick** » 1 Jun 2005 3:01 pm

Good to know...

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Tom Gorr · Post by **Tom Gorr** » 1 Jun 2005 7:20 pm

Problems

This used amp I picked up has some power amp output problems (no wonder it never had power tubes with it).

Here's the symptoms:
1) Lots of Hum
2) Guitar sound comes through fuzzyy.
3) one 'side' of the power tubes heat up to glowing and near meltdown hot (eg. one of the push or pull 'sides' - not the inside pair, or the outside matched pairs).

I can guess what's happening from a waveform point of view - one half of the signal (say, the '+' half) is clipping hard, the other half is amplifying normally.

In terms of diagnosis I am less inclined to guess. This is a Peavey Heritage VTX which has a power amp section that includes a few stages of op-amps, then a few stages of pairs of transistors in push pull configuration, including a matched transistor pair connected to the cathode of the inside power tube pair.

Any thoughts on what is most likely wrong here ? Is there any probability that its the output transformer? Hope not.

Let me know your thoughts.[This message was edited by Tom Gorr on 01 June 2005 at 08:24 PM.]

jim milewski · Post by **jim milewski** » 1 Jun 2005 8:03 pm

I had this problem with a twin, it was a 56kohm resistor connecting two pins on the output tubes, as you mentioned the two tubes were way to bright, I'll see if I can find a schematic to let you know, it was an easy fix

Tom Gorr · Post by **Tom Gorr** » 2 Jun 2005 1:13 pm

Thanks Jim,

I contacted Peavey who have indicated that this problem arises in this 'very unique design' when the transistor that feeds the cathode burns out - normally due to a tube failure/arcing.

So I ordered a replacement set of transistors.

Tom Gorr · Post by **Tom Gorr** » 27 Jul 2005 8:31 am

Thought I'd update this thread.

The Fixup to the Heritage took all of an hour to disassemble the amp and remove the two sets of transistors that drive the cathodes in the rather unique tube power amp circuit. I never even electrocuted myself. This cost $20 in parts. I do wish to brag that I got this amp for less than US$100 cause it wasn't working....and now its perfect, a buck a watt - not bad for a combo.)

I've A/B'ed the three sets of Svetlana Winged C-6L6 GC tubes I bought from the tubestore.com (excellent service BTW). These were a 17, 22 and 27. The pair of 27's breakup the nicest when the tubes are overdriven - meaning, the harmonics remain musically balanced. The lower number tubes seemed to distort the bass frequencies prior to the higher harmonics, giving a flubby sound.

Very happy with that tube. Silky smooth for steel, and has a nice grind with six-string, and works great for all out rock and roll, too, with quality preamps.

All in all - super happy with this PV hybrid.
[This message was edited by Tom Gorr on 27 July 2005 at 11:44 AM.]

Leon Grizzard · Post by **Leon Grizzard** » 31 Aug 2005 10:42 am

I have a Fender Hot Rod Deluxe, but it just doesn't have the sparkle of my '73 Twin Reverb. Would replacing the stock Groove Tubes tubes with the Groove Tubes 6l6GE's help?

Keith Cordell · Post by **Keith Cordell** » 31 Aug 2005 6:02 pm

Leon, that is the amp that I recently bought for playing guitar and lap steel through. I strongly recommend my amp techs advice on making it great;
Get an Eminence Cannabis Rex speaker. VERY nice low end, makes the amp sound much more balanced through the EQ spectrum.
Change the tubes- I got Svetlana 6L6's and EH 12AX7EH's with a Phillips 12AT7 on the phase inverter. This tube is an essential change if you are going to use the amp for any steel work, it reduces the gain that creates overdrive. For a total cost of less than $500 I have as close to a tweed Deluxe as I can afford to get, and it is a very reliable amp.
The Cannabis Rex, BTW, is a hemp cone- lovely shade of green, made me wanna look for rolling papers, LOL- and is a slower breakup than the stock speaker with a much better sound. If you can only manage one of the 2 things, I'd get the speaker. It's a pronounced improvement. [This message was edited by Keith Cordell on 31 August 2005 at 07:04 PM.]

Leon Grizzard · Post by **Leon Grizzard** » 1 Sep 2005 5:42 am

Thanks Keith. I just play guitar through it - Texas Swing. The other mod it needs is to move the knobs out of the hole in back to the front where I can see the darn things.[This message was edited by Leon Grizzard on 01 September 2005 at 06:45 AM.]

Keith Cordell · Post by **Keith Cordell** » 1 Sep 2005 6:37 am

If all you are using it for is guitar just use the 12AX7EH's. The 12AT7 is unnecessary.

jim milewski · Post by **jim milewski** » 1 Sep 2005 1:45 pm

Tom, I used my Heritage Sat nite with the Blue Marvel and Scorpion combination with fantastic results! All the power and no breakup, the guitar was a push pull, I used a Genesis 3 for effects, ya, you got a great deal, hope you like the amp

Jim Sliff · Post by **Jim Sliff** » 1 Sep 2005 6:58 pm

Groove tubes is a marketing machine. They buy the same tubes as most other suppliers and put their name on 'em - do some snake-oil and mirrors testing to "rate" them and sell them in sets at inflated prices.

The only tube they make is the 6L6GE - and most of it is actually made in China. Enough assembly is done here they can claim "made in USA".

For NEW tubes, I much prefer JJ's.

But you'd be better off going online to a NOS (New Old Stock) tube supplies like KCA NOS Tubes or "Lord Valve" and buying real GE's, Sylvanias, TungSols and the like. Not cheap, but they'll outlast the Groove tubes and IMO sound much, much better.

The only Groove Tubees I keep around are for experiments in amps I'm not sure of - if they blow, I toss 'em. Eh. No great loss.

Tom Gorr · Post by **Tom Gorr** » 2 Sep 2005 11:12 am

Jim - I bought a blue marvel that I'm going to be swapping in for 1 of the scorps. I also am wiring in a DPDT heavy duty switch to switch between the two speakers. Also some other neat mods I'm working on. This amp is an experimenters dream, and it sounds terrific.

Harold Dye · Post by **Harold Dye** » 3 Sep 2005 4:11 am

I have two MM heads. One is a 65 watt and I am unable to identify the tubes in it. The other is a 150 watt with 4 Groove Tube 6L6B. I think they may be number 5's, at least that is what is written on the tube with a pen (not stamped like other writing on the tube). Both these amps are in perfect condition but there is a difference in tone. I know different amps sound different but my concern here is the tubes. The 150 does not have the warmth the 65 has. I see from this thread GT number 7's are prefered for steel,when using GT tubes. I never play 6 string thru either of these, just steel. Any suggestions on a better sounding tube for the 150.

Jim Sliff · Post by **Jim Sliff** » 3 Sep 2005 7:07 pm

Harold - there's no way you're pulling 150 watts out of 4 6L6's. The plate voltage in those amps is also usually way too high for 6L6's - most have EL34's in the power section and still hit them with 500 volts or so.

Are you SURE those are 6L6's??

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 6 Sep 2005 7:01 am

Jim (M) and Tom,

I just picked up a Heritage VTX this weekend and so far I love it.

Two questions:
(1) The half power mode seems to be almost as powerful as the full power mode. Should that be? (Of course, I haven't dared to turn the thing up past 2 or three yet!)

(2) Any suggestions for dialing in a standard E9th tone? I play a Dekley S-10 with a stock single coil pickup. I got pretty close just going through the main channel. Anything to be gained on the phaser (2nd) channel?

Thanks!

Dan

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Dan Beller-McKenna
Durham, NH
Dekley S-10, Telecaster, Guild D-35, Peavey Heritage VTX

Keith Cordell · Post by **Keith Cordell** » 7 Sep 2005 3:05 am

Following up on earlier comments, I have had time to burn in the tubes and break in the new Cannabis Rex speaker in my amp. For a long time I have been sceptical about the value of "burn in" where tubes are concerned, I know they get a little better but with this setup they improved greatly; the speaker also opened up quite well and has even more EQ than it had when I talked about it earlier. From now on the Fender Hot Rod Series amps get this setup for me, thinking about getting another just to have around!

Tom Gorr · Post by **Tom Gorr** » 7 Sep 2005 4:32 pm

Hi Dan:

First - Run this amp with the "post-gain" controls wide open, and adjust the loudness with the pre-gain.

HALF POWER SWITCH:

Remember that in a perfectly linear situation, half power only drops the apparent loudness by 10 db, which isn't very noticeable - except in the long term (your hearing loss will be slightly lower!)

Since the power amp should be set high enough to be in power tube compression or saturation, the actual loudness change is even less than 10 db.

This switch drops the plate voltage to the power amp tubes to 275 V from 550 V. Setup your 'clean steel' sound with the pregain just to the point that the power amp is rich sounding, but not 'distorted'. When you switch to your six string, switch to low power, and voila - instant power-tube crunch.

As I see it, this feature (in conjunction with the pregain setting) allows you to go from 'power-tube compression' into 'power-tube overdrive'. The actual loudness is not a lot different, however, the contribution of power amp distortion is very evident.

Note that you can pull tube 2 and 4 (I think...) and you reduce the overall power by 50%, and the low power then reduces it again. For living room use only.

SETTINGS:
First, the scorpion speakers in the stock amp are an excellent source of rock'n'roll with a six-string - but perhaps not great for steel. I have my amp output wired to the 15" BW1502 that came with my Vegas 400. However, I have bought a Blue Marvel from Peavey that will replace one of the Scorps.

More to your point - I use the clean channel with amp on high power for steel. Settings with the output sent to the BW1502
- High at 0db
- Mids cut 4 db at 800 Hz
- Bass cut 3 db (Oops...not 'to 3db')

I use the 'lead' channel purely for six-string - as it is a fully functional EQ with the bonus of a 6L6 power amp section.

[This message was edited by Tom Gorr on 09 September 2005 at 01:19 PM.]

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 7 Sep 2005 5:53 pm

Thanks Tom; I'll try this (Jim sent a long some ideas as well: thanks!)

Dan

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Dan Beller-McKenna
Durham, NH
Dekley S-10, Telecaster, Guild D-35, Peavey Heritage VTX

Tom Gorr · Post by **Tom Gorr** » 9 Sep 2005 12:37 pm

Dan - forgot about the phaser question.

In fact, I think the phaser works on both channels ('normal' and 'lead' channels).

One of the 'features' of the amp is the ability to pull the phase knob out to fix the phase, rather than having it oscillate in the knob-in position.

For the lead channel with your Tele:
1) turn the power switch to low
2) set pregain high enough to get some power amp crunch
3) pull the mid-boost on the treble knob.
4) EQ to taste.

That's what this amp is all about. Flexibility.