An "Omage" to Harvey Gerst - D130 Question

[jackrhein]

It certainly is an honor to have my first query answered by the big man himself, Wow! Thanks Harv.
I have another question: I want to use a d130 to replace the two 12 Jensens in my 1965 silvertone 1484 piggy back amp. (It has two 6L6's in a push pull circuit, but I don't know how many ohms the amp is looking for) I don't know if I should use a 16 ohm or a 8 ohm speaker. The problem is that the amp is too loud for my requirements so i was thinking of using a 16 OHM speaker to soak up some of the power. I read some other missives about the cab size and sound deadening material which I will also incorporate but I still need to get the amp up to "3" or "4 " to get the full amp character.

[jackrhein]

i wonder why my original thread was moved

[Titanium Dome]

It was in the wrong forum.

Originally, you posted it (twice) in the "Music" forum in "Lansing Related Forums." The content of your thread really is about a Lansing product, D130, and some do-it-yourself modifications, so it was moved here. In moving it, the double posting was eliminated, too.

So it was a little bit of housekeeping, nothing more.

Just to be very clear, I PMed a moderator and suggested he look at the posts and move them to an appropriate place. I don't know if anyone else mentioned, too. Whatever the case, the intent was just to get the thread into the right forum.

Hope this helps. :)

[Harvey Gerst]

It certainly is an honor to have my first query answered by the big man himself, Wow! Thanks Harv.
I have another question: I want to use a d130 to replace the two 12 Jensens in my 1965 silvertone 1484 piggy back amp. (It has two 6L6's in a push pull circuit, but I don't know how many ohms the amp is looking for) I don't know if I should use a 16 ohm or a 8 ohm speaker. The problem is that the amp is too loud for my requirements so i was thinking of using a 16 OHM speaker to soak up some of the power. I read some other missives about the cab size and sound deadening material which I will also incorporate but I still need to get the amp up to "3" or "4 " to get the full amp character.First, we hafta figure out what the load is now, so get a multi meter and measure the DC resistance of the speakers. Then, we can work from there.

[duaneage]

IIRC tube amps don't like higher impedance loads. If it is too loud could you just adjust the gain down a bit or does this amp go to 11?

[jackrhein]

It had 2 jensen 8 ohm speakers wired in parallel which it would have made the amp originally looking for a 4 ohm load. Do think a 16 ohm load would change change the tone or fry the output transfromer?.

[Zilch]

Well, we've got one post that tube amps don't mind higher impedance loads, and one that says they don't mind them.

[Somebody gotta get definitive soon.... :p ]

[jcrobso]

It certainly is an honor to have my first query answered by the big man himself, Wow! Thanks Harv.
I have another question: I want to use a d130 to replace the two 12 Jensens in my 1965 silvertone 1484 piggy back amp. (It has two 6L6's in a push pull circuit, but I don't know how many ohms the amp is looking for) I don't know if I should use a 16 ohm or a 8 ohm speaker. The problem is that the amp is too loud for my requirements so i was thinking of using a 16 OHM speaker to soak up some of the power. I read some other missives about the cab size and sound deadening material which I will also incorporate but I still need to get the amp up to "3" or "4 " to get the full amp character.

Most guitar speakers have a sensitivity rating of 92~95db. Lets say the Jensen's are 94db for one speaker, two speakers will give 97 db. The sensitivity for a D130 is 101db, so the amp will play louder with the D130.

I suggest that you get a 100W 8 Ohm L-pad connect this between the amp and the speakers. The amp will see 8 Ohms and you can turn down the speakers to a lower level. If you want to use a D130 to get better over all sound GO FOR IT!!!:) John

[4343]

Well, we've got one post that tube amps don't mind higher impedance loads, and one that says they don't mind them.

[Somebody gotta get definitive soon.... :p ]

Maybe not definitive, but "hear" goes...

Rules of thumb:

SS Amps don't like Shorts, Tubes/Valves don't mind so much.
Tube/Valve Amps don't like Opens, Solid State don't mind at all in most cases.

Me, I wear shorts in the open, most of the year...:blink:

There are several commercial products designed to lower the level to the speakers, "Power Soak" by Tom Sholtz for instance.

[Hamilton]

Tube amps don't care for a load mismatch, but will tolerate them....to a point.

With a low impedance load the tubes will be forced to put out more current as the volume goes up since the load is closer to a short : thus tube life will be shortened.

In high impedance loads, and as the volume goes up, there is the danger of flyback, which are high voltage spikes that can arc through the output transformer insulation, across tube sockets or inside the tubes themselves. Once an arc has occured...it will probably happen again...and again.

If it's impossible to have the correct match, a lower load might be the safer bet. Leo went that way with the external speaker jack on his Fender amps.

[Allanvh5150]

Well, we've got one post that tube amps don't mind higher impedance loads, and one that says they don't mind them.

[Somebody gotta get definitive soon.... :p ]

I will give you a definative answer. It depends very much on the clever guy that designed the output transformer. Having the correct impedence load on the output transformer will result in a better power transfer. If you use a mismatched load the power transfer won't be as good. It generaly wont harm most amplifiers and it could result in a different sound that is to your liking.:)

[duaneage]

Since speakers are not a flat resistive load across the deck the best thing to do is sweep the speaker system and plot the impedance to see what the max and minimum impedance is. The WT2 (Woofer Tester 2) can plot this in about 60 seconds and also give phase relationships as well.

From this you can compare two systems and see what the difference is. Makes more sense than guessing, or asking everyone what they "think" will happen. If you post the curves from these tests the group of experience here can make recommendations, including modifications.

Too many times posters ask for someone to measure a cab or a duct tube and then merely duplicate. The right approach is to measure and adjust until it's right. I've never had a system match simulated designs exactly, there are too many variables.

[Beowulf57]

I've been driving a D130 & a D131 (ostensibly 16 ohms, but measure 6.3 ohms DCR) both with and without networks using 30 watt P-P tube amps for over 40 years. My Peerless OT's are set to the 16 ohm taps and I have never had any problems. Tube amplifiers are voltage amplifiers and as was noted, when you drop the load impedance below nominal, more current is demanded of the output stage and the OT. Unless you drive the amp hard, it is unilkely to cause any problem. Some people like to use a low impedance OT tap as this means less wire is in the OT secondary..."purer" sound? Hmm, not likely to be audible IMO. Note that if you have NFB (almost all tube amps of that era do) taken from the OT secondary circuit in your amp design, changing the load impedance will change the amount of loop feedback (in my amps this is fully adjustable, so no issue). This will certainly alter the sound and even possibly the stability of the amp

As someone also noted, the D130 is a very high sensitivity speaker (mine are rated at 103dB/W/M) and thus you are likely to get an increase in output level. I believe the Silvertone 1484 is a 100 watt unit? Way more than you should ever need...in fact you could overdrive the D130. Rather than adding an attenuator at the output (which will soak up alot of power unnecessarily), you could consider adding 10 dB inline RCA attenuators to your source inputs to the amp and reduce the level more efficiently. Running the D130 from a lower impedance output tap is not that likely to effectively lower the output level. You could also check the OT's on your amp...perhaps there are different impedance taps, but again this is not an effective method of reducing output level.

[Beowulf57]

Okay...I found a schematic for the 1484. It certainly doesn't produce 100 watts (so no problem there) with only 2 6L6GC's and there is no overall loop feedback from the secondary. As well there is only one output tap on the transformer...I'd go with he 8 ohm D130 and input level attenuators.

[duaneage]

I think the 100 watt assumption came from power consumption ratings at the wall, more like 35 watts audio output. Still enough for decent volume from a pair of 12's

[jcrobso]

Okay...I found a schematic for the 1484. It certainly doesn't produce 100 watts (so no problem there) with only 2 6L6GC's and there is no overall loop feedback from the secondary. As well there is only one output tap on the transformer...I'd go with he 8 ohm D130 and input level attenuators.
The two Jensen speakers are 8 ohm giving a 4 Ohm load.
The schematic shows +475 volts on the plate, this could give you a max of about 50watts RMS. As others have stated for maximum power transfer the load should be the same as the output impedance of the transformer. I don't feel that 16 Ohms should be problem. You could get 8 Ohm 100w L pad then the amp would see 8 Ohms and you can reduce the level and run amp up in the range where it sounds good.:) John

[sba2]

Hi, I've been searching this site for the T-S parameters on the JBL d130f, but have not had any luck. I'd appreciate any help. Thanks

[SMKSoundPro]

JBL PROFESSIONAL
THIELE SMALL LOW FREQUENCY DRIVER
PARAMETERS AND DEFINITIONS
April 2, 2005
Page 4 of 5
MODEL FS QTS QMS QES VAS EFF PE XMAX RE LE SD BI MMS FLUX
D130 40 0.25 4 0.27 297.3 6.7 75 0.76 6.3 0.6 0.090 18 60 1.2

[SMKSoundPro]

JBL PROFESSIONAL

THIELE SMALL LOW FREQUENCY DRIVER
PARAMETERS AND DEFINITIONS

April 2, 2005
Page 4 of 5

MODEL FS QTS QMS QES VAS EFF PE XMAX RE LE SD BI MMS FLUX
2231H 16 0.21 5.5 0.22 736.2 1.4 100 5.08 6.3 1.4 0.088 21 151 1.2
2234H 23 0.22 2 0.25 458.7 2.1 150 8.38 6 1.2 0.090 20.5 105 1.2
2235H 20 0.25 2.5 0.28 458.7 1.3 150 8.38 6 1.2 0.090 20.5 155 1.2
2240G 30 0.25 2.5 0.25 481.4 5 300 5.59 2.5 0.7 0.130 17.1 164 1.22
2240H 30 0.23 2.2 25 481.4 5 300 5.59 6 1.4 0.130 25 164 1.22
2241G 35 0.4 5.7 0.43 311.5 2.9 600 7.62 2.5 0.86 0.123 13.6 145
2241H 35 0.4 5.7 0.43 311.5 2.9 600 7.62 5 1.75 0.123 19.2 145
2242H 35 0.28 5 0.29 282.3 4 800 7.87 4.7 1.25 0.124 23.7 158
2245H 20 0.27 2.2 0.27 821.2 2.1 300 9.65 5.8 1.4 0.130 21 185 1.22
2250H 188 0.47 4.5 0.53 1.67 2 350 3 5.2 1 0.0204 17 25 1.0
2250J 185 0.45 4.8 0.47 1.5 2.3 350 3.0 8.7 1.7 0.0204 22.5 24 1
2251J 61 0.2 4 0.21 1.011 2.89 388 5.7 12.65 0.031 26.77 0.032
2254J 46.63 0.16 2.47 0.17 2.60 4.20 600 6.35 11.16 0.063 10.99 0.088
2255H 39 0.30 3.68 0.33 170 2.9 650 8 5.0 1.5 0.088 20.1 109
2256G 24.2 0.47 7.79 0.5 138.5 600 20.3 3.1 0.7 0.078 15.7 284
2258H 31 0.27 4.82 0.28 407 800 8 5.2 1.24 0.124 22.3 140
2262H 56.2 0.34790.39 42.2 2.2 700 8 5.2 0.055 18 68.0
2265H 37 0.32 3.3 0.36 176 2.5 750 8 5.1 1.7 0.088 19.5 112 0.6
2266H 31 0.37 4.8 0.4 110 0.8 700 11 4.8 2.63 0.088 24.7 260 0.6
2268H 33 0.36 3.8 0.39 328 2.8 800 23 5.3 1.85 0.1269 21.5 168 0.6
D123 45 0.45 4.5 0.5 135.9 2.5 50 2.54 6 0.5 0.053 12.4 45 1
D130 40 0.25 4 0.27 297.3 6.7 75 0.76 6.3 0.6 0.090 18 60 1.2
D131 50 0.18 8.5 0.18 127.4 8.4 75 0.76 6.3 0.5 0.053 18 35 1.2
D208 60 0.31 3.5 0.34 34.0 2.1 25 2.54 6 0.3 0.021 6.8 11 0.85
E110 65 0.36 4 0.4 45.3 3 75 2.54 6 0.4 0.032 12.1 21 1.03
E120 60 0.17 1.8 0.19 79.3 8.6 150 3.05 6.3 0.4 0.053 21.7 36 1.35
E130 40 0.19 1.8 0.21 297.3 8.6 150 2.54 6.3 0.4 0.090 21.1 60 1.35
E140 32 0.17 5 0.19 297.3 4.9 200 3.56 5.5 1.11 0.090 24.1 94 1.35
E145 35 0.25 6 0.26 274.7 4.3 150 7.11 5.7 1.6 0.090 16.1 55 0.97
E155-4 30 0.2 2.2 0.22 424.8 4.9 300 5.08 2.5 0.7 0.114 17 125 1.22
E155-8 30 0.2 2.2 0.22 424.8 4.9 300 5.08 6 1.4 0.114 25 125 1.22
G125-8 65 0.32 5.5 0.34 70.8 5.5 200 2.54 5.2 0.5 0.053 13.7 37 0.98
G135-8 45 0.36 5.5 0.38 235.0 5.5 200 2.54 5.2 0.5 0.090 13.7 60 0.98
G135-A 45 0.48 6.6 0.51 218.0 3.8 200 6.10 6 0.75 0.090 15.8 60 0.98
K110 65 0.36 4 0.4 45.3 3 75 1.52 6 0.4 0.032 10.3 17 1.02
K120 50 0.2 4 0.21 121.8 6.9 100 1.52 6.3 0.6 0.053 18 35 1.2
K130 40 0.25 4 0.27 297.3 6.7 125 0.76 6.3 0.6 0.090 18 60 1.2
K140 30 0.21 5 0.22 297.3 3.5 150 5.08 5.5 1.3 0.090 22.3 105 1.2
K145 35 0.29 6 0.3 243.5 3.4 150 5.08 8.8 2.2 0.079 21.7 75 0.9
K151 30 0.27 6 0.28 365.3 3.4 150 2.54 6 2 0.107 22 125 1.2
LE5-10 250 1 3 1.6 0.7 0.69 25 1.52 6 0.05 0.006 4.3 3 1.3
LE8T 45 0.49 4 0.55 34.0 0.5 25 4.57 5.5 0.3 0.018 6.2 16 0.85
LE8TH 45 0.56 4 0.65 34.0 0.5 25 5.59 5.5 0.3 0.018 6.2 16 0.85
LE10A 30 0.41 6 0.44 101.9 0.6 75 6.10 4.4 0.6 0.032 8.1 35 1.02
MODEL FS QTS QMS QES VAS EFF PE XMAX RE LE SD BI MMS FLUX
88

[sba2]

SMKSoundPro, Thank you very much for posting the T-S parameters.