Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Cabinets-Speakers => Topic started by: firemedic on September 19, 2011, 08:25:40 am

Title: Reverberocket 2 speaker replacement
Post by: firemedic on September 19, 2011, 08:25:40 am

I need opinions. I'm fixing to replace the stock 12" speaker in my drummer's '65 reverberocket 2. It has 2- 7591a tubes for output. According to the Weber bias calc. site, they are pushing @22W each, which exceeds the datasheet spec for this tube. They are not redplating. I replaced the 140R stock cathode resistor with a 150R to account for the higher voltages it is seeing now.
I don't believe it's actually pushing 44W.
I'm torn between a WGS 30W Reaper, and a Weber 25W Signature 12S alnico. I'm not going to spend more than $80 for the speaker. Any opinions on this?   

Title: Re: Reverberocket 2 speaker replacement
Post by: firemedic on October 16, 2011, 09:58:08 pm

Okay, well I went with a Jensen RI C12Q. Sounds pretty good.

Title: Re: Reverberocket 2 speaker replacement
Post by: PRR on October 25, 2011, 11:49:53 pm

> they are pushing @22W each

Tube-heat is NOT output power.

Figuring the tube heat is like judging a car's power by the heat coming off the engine. They are related (300HP truck throws a lot more heat than 16HP lawnmower) but efficiency leverage has a lot of effect.

Two 7591 would not be used for less than 30W and won't make much over 45W within ratings. Cathode-bias maybe 35W.

25W speaker is too little, go 50W for reliability.

I would not fret over-much about 22W Pdiss on recent-made 7591. The original 19W spec was conservative and AFAIK modern reproductions are built with mostly 6L6GC bits and pieces. Because of the delicate G1 structure, you do not want to try for 35W Pdiss, but 22W is perhaps reasonable for a stage-amp.

Title: Re: Reverberocket 2 speaker replacement
Post by: firemedic on October 28, 2011, 08:18:05 am

I was also judging/guessing by the apparent power coming out the speaker when choosing a speaker, which with the stock OT was not very impressive.
Since my post I have replaced the entire output section (041318 OT, C12Q speaker, 7591AEH tubes, cathode resistor, increased bypass cap to 50uf).

The OT made the single biggest difference in the amp's volume. And it fit the old OT's footprint, no drilling required!

It sounded a little harsh at first but the speaker & tubes must be broken in because right now, this amp is ALL SWEET SPOT. No matter where I turn the knobs it sounds amazing. 

I have the original tubes, OT & speaker boxed away in the unlikely event I need to sell the amp.

The C12Q is 35W rated, also I don't usually turn it up past 7 or so. So I feel good about it.